[PATCH] msxml3: Handle SAX tags and characters for mxwriter domdoc.

[Jefferson Carpenter]

Moved some code from mxwriter ISAXContentHandler implementation into 
free functions that can be swapped out for DOMDocument functions.

For other mxwriter callback functions, immediately return E_NOTIMPL if 
the destination is a DOMDocument.

Added test_mxwriter_domdoc_start_end_document to help check the 
implementation of DOMDocument locking.

Added "BOOL locked" to XML documents and a private interface that allows 
this variable to be set and checked.  (This variable is not used thread 
safely.  `LONG refs` is thread safe, but `struct list orphans` is not.)

thanks,
Jefferson