handler would cause a segfault. This merges in Expat's lib/xmlparse.c
revisions 1.154 and 1.155, which fix this and a closely related problem
(the later does not affect Python).
Moved the crasher test to the tests for xml.parsers.expat.
The problem was that pyconfig.h was being included before some system headers
which caused redefinitions and other breakage. This moves system headers
after expat_config.h which includes pyconfig.h.
