bug#8600: Merged fixes for 8600, 8601, 8602, and (partially) for 8545

[Paul Eggert]

I committed to the Emacs trunk a merge (bzr 104134) that has fixes for
the following bugs:

* Bug#8600 - The fix removes the garbage element of code_space.

* Bug#8601 - Here I assumed that the "* 2" is a typo.

* Bug#8602 - This fixes some large-int-to-float screwups in
             the Lisp reader.

* Bug#8545 - This fixes the bug where the code should have called
             va_copy, but didn't.  Also, I changed a limit so that
             the MOST_POSITIVE_FIXNUM limit for strings applies to
             their length, i.e., does not include the null termination
             byte.  Stefan hasn't had time to chime in, but if this
             last change turns out to be incorrect I will back it out.

This merge doesn't entirely fix Bug#8545, so I'll leave that bug open;
the others I'll close.