ObjC parser simplification

[Stan Shebs]

Neil Booth wrote:
> 
> This patch removes two areas of duplication in the ObjC parser; nearly
> identical code handled the'-' and '+' method type specifiers.  It
> factors them out into a separate production, and collapses both
> duplications into one of each.

Looks good, although I have this teeny bit of apprehension about
some trickiness I'm missing. :-)

> Bootstrapped x86 Linux.  OK to commit?

Bootstrapping doesn't actually tell you much, since cc1obj never
gets run (as far as I know).  You should be able to build libobjc
and run the little ObjC testsuite, which would be pretty definitive
for this change.  If you did that, I would be totally comfortable
with the patch.

Stan