git-gui: Allow spaces in path to 'wish'

If the path of our wish executable that are running under
contains spaces we need to make sure they are escaped in
a proper Tcl list, otherwise we are unable to start gitk.

Reported by Randal L. Schwartz on #git.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -4134,7 +4134,7 @@ proc do_gitk {revs} {
 	# -- Always start gitk through whatever we were loaded with.  This
 	#    lets us bypass using shell process on Windows systems.
 	#
-	set cmd [info nameofexecutable]
+	set cmd [list [info nameofexecutable]]
 	lappend cmd [gitexec gitk]
 	if {$revs ne {}} {
 		append cmd { }