GNU Emacs bugfix commit

[Sun Yijiang]

When Emacs' frame title format is set to buffer-file-name, and there
are chinese characters in it, the title will loss characters.  The
number of the lossed characters is exactly the number of chinese
characters in the title.  This is cause by the miscalculated variable
`prec' in function `display_mode_element' in xdisp.c.  The current
source uses function `chars_in_tex' which returns the number of
characters in the string, but what we really need is the string's
width (you see, that's why), so I think this guy should be replaced
with `strwidth'.  I've made a test, and then everything is OK.

Sun Yijiang <sunyijiang@gmail.com>