git-gui: Gracefully fall back to po2msg.sh if msgfmt --tcl fails
git-gui: Gracefully fall back to po2msg.sh if msgfmt --tcl fails

Mac OS X Tiger may have a msgfmt available but it doesn't understand
how to implement --tcl.  Falling back to po2msg.sh on such systems
is a reasonable behavior.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git