rollback: improve readability; clarify that the return value is an int.

demandimport: determine at load time if __import__ has level argument

win32: quietly ignore missing CreateHardLinkA for Wine

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.