git-gui: Include our Git logo in the about dialog

Most applications tend to have some sort of pretty image in the
about dialog, because it spruces the screen up a little bit and
makes the user happy about reading the information shown there.
We already have a logo in the repository selection wizard so we
can easily reuse this in the about dialog.

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

lib/about.tcl

@@ -9,6 +9,7 @@ proc do_about {} {
 	toplevel $w
 	wm geometry $w "+[winfo rootx .]+[winfo rooty .]"
 
+	pack [git_logo $w.git_logo] -side left -fill y -padx 10 -pady 10
 	label $w.header -text [mc "About %s" [appname]] \
 		-font font_uibold
 	pack $w.header -side top -fill x