bug#18196: 24.4.50; crash when setting face background in terminal frame

[martin rudalics]

> Steps to reproduce:
> 1. build emacs from trunk (the crash does not occur on the emacs-24
> branch)
> 2. emacs -Q -nw
> 3. M-: (set-face-attribute 'default nil :background "blue")
>
> Backtrace:
> (gdb) bt full
> #0  terminate_due_to_signal (sig=sig@entry=6, 
> backtrace_limit=backtrace_limit@entry=40) at emacs.c:359
> No locals.
> #1  0x00000000004f4e77 in emacs_abort () at sysdep.c:2198
> No locals.
> #2  0x000000000049ea53 in cmcheckmagic (tty=0x6, tty@entry=0x13c6ce0) at 
> cm.c:120

This is bug#18136 hitting again.  I'm on it but it may take some time.

Thanks, martin