This patch is an implementation of bug/feature request
# 552297. It implements the simplified version
of the original proposal.
The skippedEntityHandler is called in two situations:
1) An entity reference is encountered for which no
declaration has been read *and* this is not an error.
2) An internal entity reference is read, but not expanded,
because XML_SetDefaultHandler has been called.
The attached Diff file is based on expat.h rev. 1.22
and xmlparse.c rev. 1.41.