Probably the last rollup patch for a while; I need to move on to code
reviewing.

Here's a list of changes in this patch:

* I added the oft-requested "rename the C variable for a parameter"
  functionality.  That works as follows:

     os.rename
         path as stinky: path_t

  Here the Python name is "path", and the C name is "stinky".
  Internally the "name" of the parameter is the Python name, and
  the "name" of the converter is the C name.  (But the converter
  gets the Python name too, because it needs it sometimes, e.g.
  for the keywords array.)

* Fixed a minor but difficult-to-fix problem: when cloning a function,
  the cloned function would still refer to the original function's
  name.  (You can see this in the PATH_T_INITIALIZE macros in
  os_replace in posixmodule.c.)

* While fixing the above I stumbled over a new problem: rendering
  often changes internal state of a parameter, which could cause
  problems if we clone an already-rendered parameter object.  The
  solution: make a copy of all the Parameter objects before rendering,
  then render from the copies.

* Fixing the above forced me to add a new initalizer to CConverter
  objects: pre_render(), which is called just before rendering.

* This change also means it's pretty important to call up to the super()
  for converter_init() and pre_render().

* Fixing the above also required new semantics for converter_init():
  you are no longer permitted to examine the function object in
  that method.  (I made it fail noisily with a "LandMine".)

* "clinic.py --converters" was broken, I fixed it.  (It was confused
  by object_converter having format_unit=None.)

* I fixed the unit tests too.

* You can now specify blank lines between directives without Clinic
  getting angry at you.

* I redid how I store all those little C code snippet template.
  Originally they were inline, but flush left, and that made
  reading them tiresome--the indent was jumping around on you.
  Changing to a central list removed the jumping around but now
  you had to scroll back and forth to correlate the template with
  where it was used.  The final solution: have them inline again,
  but indented, and simply outdent the text before use.  Go ahead,
  tell me that's *not* an improvement.  :D  (The outdenting function
  uses functools.lru_cache, so processing is really no slower.)

And last but certainly not least...!

Following a suggestion by Serhiy Storchaka, Argument Clinic is now
incredibly sophisticated with respect to #if'd out code.  In less than
200 lines, I wrote a reasonable C preprocessor monitor class.  The
monitor parses C files in parallel to Argument Clinic.  At any time
you can ask the monitor "what's the current preprocessor conditional
state?"  If the current code is potentially if'd out, Argument Clinic
uses the same conditional to potentially #if out the parser function,
the docstring, etc, when writing those to buffer or file.  It even
adds this to the end:

  #ifndef YOUR_FUNCTION_METHODDEF
      #define YOUR_FUNCTION_METHODDEF
  #endif /* !defined(YOUR_FUNCTION_METHODDEF) */

But *only* when necessary.

You can see this in action in the diff for Modules/clinic/zlibmodule.c.h.

I think this is a huge improvement!  (Thanks for the suggestion, Serhiy!)

Updated the patch.

* The "methoddef_ifndef" template is now sent to the "buffer"
  destination by default.  I expected posixmodule to have an #ifndef,
  I was surprised to find _import had one too.  Both files touched
  to move the buffer to an appropriate spot.

* Fixed the "original" "preset" so it explicitly sets all three new
  templates just like the actual default.

* Forgot a minor fix that was in revision 1: when generating the
  docstring for a function using optional groups, suppress the
  "self/type/module" first argument in the signature.  (The signature
  isn't parsable by inspect.Signature, so we go ahead and insert
  something user-readable like the docstrings before Argument Clinic
  used to do.)
  
* Changed _dbm.dbm.get to no longer use optional groups.  Why was it
  doing that in the first place?  There's now exactly one function
  checked in using optional groups, curses.window.addch.

New changeset 19d81cc213d7 by Larry Hastings in branch 'default':
#Issue 20456: Several improvements and bugfixes for Argument Clinic,
http://hg.python.org/cpython/rev/19d81cc213d7

Checked in!  I think that's the last new feature for Argument Clinic until after 3.4 ships.

The converters argument in command line is still broken.

[sky@localhost cpython3.4]$ hg pull -u
pulling from http://hg.python.org/cpython
searching for changes
no changes found
[sky@localhost cpython3.4]$ ./python Tools/clinic/clinic.py --converters

Legacy converters:
Traceback (most recent call last):
  File "Tools/clinic/clinic.py", line 4131, in <module>
    sys.exit(main(sys.argv[1:]))
  File "Tools/clinic/clinic.py", line 4063, in main
    print('    ' + ' '.join(c for c in legacy if c[0].isupper()))
  File "Tools/clinic/clinic.py", line 4063, in <genexpr>
    print('    ' + ' '.join(c for c in legacy if c[0].isupper()))
IndexError: string index out of range

Unit test for exercising Tools/clinic/clinic.py using assert_python_ok would be good, but that deserves a dedicated ticket.

Here is the patch to fix the bug.