scandir-3.patch: New implementation based on scandir-2.patch on Ben's github repository.

Main changes with scandir-2.patch:

* new DirEntry.inode() method

* os.scandir() doesn't support bytes on Windows anymore: it's deprecated since python 3.3 and using bytes gives unexpected results on Windows


As discussed with Ben Hoyt, I added a inode() method to solve the use case described here:
https://www.reddit.com/r/Python/comments/2synry/so_8_peps_are_currently_being_proposed_for_python/cnvnz1w

I will update the PEP 471 to add the inode() method.


Notes:

* os.scandir() doesn't accept a file descriptor, as decided in the PEP 471.

* It may be nice to modify Scandir.close() to close the handle/directory; Scandir is the iterator returned by os._scandir()

* My patch doesn't modify os.walk(): it prefer to do that in a new issue

* DirEntry methods have no docstring


Changes with scandir-2.patch:

* C code is added to posixmodule.c, not into a new _scandir.c file, to avoid code duplication (all Windows code to handle attributes)
* C code is restricted to the minimum: it's now only a wrapper to opendir+readdir and FindFirstFileW/FindNextFileW
* os._scandir() directly calls opendir(), it's no more delayed to the first call to next(), to report errors earlier. In practice, I don't think that anymore will notify :-p
* don't allocate a buffer to store a HANDLE: use directly a HANDLE
* C code: use #ifdef inside functions, not outside
* On Windows, os._scandir() appends "*.*" instead of "*" to the path, to mimic os.listdir()
* put information about cache and syscall directly in the doc of DirEntry methods
* remove promise of performances from scandir doc: be more factual, explain when syscalls are required or not
* expose DT_UNKOWN, DT_DIR, DT_REG, DT_LNK constants in the posix module; but I prefer to not document them: use directly scandir!
* rewrite completly unit test:

  - reuse test.support
  - compare DirEntry attributes with the result of functions (ex: os.stat() or os.path.islink())

* add tests on removed directory, removed file and broken symbolic link
* remove ":" from repr(DirEntry) result, it's now "<DirEntry 'xxx'>"; drop __str__ method (by default, __str__ calls __repr__)
* use new OSError subclasses (FileNotFoundError)
* DirEntry methods: use stat.S_ISxxx() methods instead of "st.st_mode & 0o170000 == S_IFxxx"