Ensure unparsed entity handler gets set
Ensure unparsed entity handler gets set

Revise dummy handlers to flag when they are executed, and ensure
that they are executed in the test.  Add XML to get the deprecated
unparsed entity handler executed, and ensure that the allocation
check fails each possible allocator in sequence despite the
caching of some allocations in the parser object.

NOTE that this commit does not pass check because of an allocation
bug.

libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat,libexpat/libexpat