Make the `vtmode' config option work under X. In the process I've

had to move another of its values out into wincfg.c - paradoxically,
this was the `font has X encoding' option! (Because the Unix font
handling code expects to be able to tell for _itself_ whether it has
a font with X-encoded line drawing glyphs.)

git-svn-id: svn://svn.tartarus.org/sgt/putty@3145 cda61777-01e9-0310-a592-d414129be87e