I'm checking this in.

It is not ok to 'return' from inside a TRY_CATCH.  This messes up the
cleanups and will lead to problems later.

I found this problem using the attached script.  It is simplistic but I
think it should catch most cases of this bug.  You can run it using:

    emacs --script try-catch.el /path/to/src/gdb

Tom