Merge with PyXML 1.71:

Merge with PyXML 1.71:
60: Added support for the SkippedEntityHandler, new in Expat 1.95.4.
61: Added support for namespace prefixes, which can be enabled by setting the
    "namespace_prefixes" attribute on the parser object.
65: Disable profiling changes for Python 2.0 and 2.1.
66: Update pyexpat to export the Expat 1.95.5 XML_GetFeatureList()
    information, and tighten up a type declaration now that Expat is using
    an incomplete type rather than a void * for the XML_Parser type.
67: Clarified a comment.
    Added support for XML_UseForeignDTD(), new in Expat 1.95.5.
68: Refactor to avoid partial duplication of the code to construct an
    ExpatError instance, and actually conform to the API for the exception
    instance as well.
69: Remove some spurious trailing whitespace.
    Add a special external-entity-ref handler that gets installed once a
    handler has raised a Python exception; this can cancel actual parsing
    earlier if there's an external entity reference in the input data
    after the the Python excpetion has been raised.
70: Untabify APPEND.
71: Backport PyMODINIT_FUNC for 2.2 and earlier.