Merge with 1.25 of PyXML:

Participate in garbage collection if available.
Potentially decref handlers in clear_handlers.
Partially reindent.
Put synthetic frame object on the stack to support better error output.
Expose Python codecs to pyexpat.
Add new Expat 1.2 handlers and API.
Fix memory leak: release self->handlers.
Do not expect PyModule_AddObject and PyModule_AddStringConstant in 2.0b1.
Raise exception in ParseFile.