Spring cleanup ...:
- configure.in Makefile.am config.h.in xmlversion.h.in: detect if
  we need string functions
- trio.[ch] strio.[ch]: embedded the Trio-0.23 string functions
  to be able to use them where needed. Applied some changes
  to reduce name linking pollution and compile in only what's
  needed.
- HTMLtree.c debugXML.c entities.c error.c nanoftp.c valid.c
  xlink.c xmlversion.h.in xpath.c: got rid of the #ifdef
  for the string manipulation functions
- xmlmemory.[ch]: removed DEBUG_MEMORY_FREED and added it automatically
  to the free() function of xmlmemory.c
- entities.c HTMLtree.c parserInternals.c tree.c uri.c valid.c
  xinclude.c xmlIO.c xpath.c xpointer.c: removed the MEM_CLEANUP
  usage.
Daniel