Updated patch, removing the FIXMEs, and slightly reworking the test code.

I've wrapped the whole of get_frame_marker_info with a PyErr_Fetch/PyErr_Restore pair: the PyUnicode_AsUTF8String calls could fail with a MemoryError, and we don't want to confuse the regular exception handling within ceval.

I'm not sure how to write a unit test to test for this: perhaps we could corrupt the __code__ instance so that co_filename is not a PyUnicodeObject, leading to a TypeError within the function, but that's a readonly attribute.  Any ideas?

I've also added a unit test for a non-ASCII script (Lib/test/systemtap_sample_☠.py), containing a non-ASCII identifier (文字化け).

The non-ASCII script name (Lib/test/systemtap_sample_☠.py) may be controversial: do we have anything like that in the source tree yet?  Is there any risk of messing up the build across platforms, or of impacting the Hg migration?

Still to-do:
  - address the "Undefined symbol" issues seen by jcea.
  - documentation
  - doublecheck performance