Fix some "comparison is always true/false" warnings.

Fix some "comparison is always true/false" warnings.

On Cygwin the wchar_t type is an unsigned short (16-bit) int.
This results in the above warnings from the return statement in
the wcwidth() function (in particular, the expressions involving
constants with values larger than 0xffff). Simply replace the
use of wchar_t with an unsigned int, typedef-ed as ucs_char_t.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>