The COMPOUND_TEXT encoding used by some X applications to transfer

The COMPOUND_TEXT encoding used by some X applications to transfer
internationalised text in selections is a subset of ISO 2022
containing no base character sets which libcharset doesn't already
support. As such, it isn't too hard to add direct compound text
support into libcharset, so here it is. With any luck I should
eventually be able to integrate this into Unix PuTTY, to deal with
the fact that the useful Xutf8 functions we currently use are
specific to XFree86.

git-svn-id: svn://svn.tartarus.org/sgt/charset@4578 cda61777-01e9-0310-a592-d414129be87e