osutil: avoid accidentally destroying the True object in isgui (
issue2937)
Needed to use 'Py_RETURN_TRUE' instead of 'return Py_True' to avoid
reference count errors which would randomly crash the Python
executable during merge. This only happened when you had something
configured in merge-tools and the merge was large enough.
bundlerepo: add argument check before unlink
The default argument value of None, for bundlename, would cause an exception.
Callers currently pass an empty string, thus dodging this problem.