git-gui: detect the use of MUI langauge packs on Windows
The Tcl msgcat package doesn't detect the use of a multi-lingual language pack on Windows 7. This means that a user may have their display language set to Japanese but the system installed langauge was English. This patch reads the relevent registry key to fix this before loading in the locale specific parts of git-gui.
Signed-off-by: Pat Thoyts <firstname.lastname@example.org>