[0/27] RFC: fix reports from the CPython checker

[Tom Tromey <tromey at redhat dot com>]

The Python plugin for GCC comes with an analyzer that checks the usage
of the CPython API:

https://gcc-python-plugin.readthedocs.org/en/latest/cpychecker.html

I ran this checker on gdb and fixed a number of bugs that it pointed
out.

Unfortunately the checker still has a large number of false reports.
Some of these are due to oddities in gdb -- cleanups mostly -- but some
are bugs in the checker itself.  I've filed bug reports against the
checker (and fixed some bugs as well); and will file more later.

I built and regtested this series on x86-64 Fedora 18.

I think most of the patches are pretty obvious.

I intend to run the checker periodically and fix problems.  I don't
think we can reasonably require it for changes in the Python code, due
to all the false reports :-(

Tom