Stop general_textout() from trying to slice up the input clipping

Stop general_textout() from trying to slice up the input clipping
rectangle into smaller ones: it doesn't work any more, since the new
variable-pitch code can now call general_textout() with a larger
clipping rectangle than the text it's meant to be displaying. Instead,
general_textout() now uses the same semantics as the next loop up in
do_text_internal(): the first piece of text it displays uses the
opacity setting passed in, which blanks the entire clipping rectangle
if necessary, and then subsequent overlays are non-opaque. And the
same clipping rectangle is used throughout.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9067 cda61777-01e9-0310-a592-d414129be87e