git-gui: Include the Tcl/Tk version in the about dialog.

Users may need to know what version of Tcl they are running git-gui
under, in case there is an interesting interface quirk or other
compatability problem we don't know about right now that we may
need to explore (and maybe fix).  Since its simple enough to show
a line with this version data we should do so.

We also try to reduce the amount of text shown as often the Tcl and Tk
version numbers will be identical; when this happens we should only show
the one version number.

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

git-gui

@@ -9,8 +9,7 @@ All rights reserved.
 
 This program is free software; it may be used, copied, modified
 and distributed under the terms of the GNU General Public Licence,
-either version 2, or (at your option) any later version.
-}
+either version 2, or (at your option) any later version.}
 
 set appname [lindex [file split $argv0] end]
 set gitdir {}
@@ -2166,6 +2165,7 @@ proc do_commit {} {
 
 proc do_about {} {
 	global appname copyright
+	global tcl_patchLevel tk_patchLevel
 
 	set w .about_dialog
 	toplevel $w
@@ -2193,8 +2193,17 @@ $copyright" \
 		-font font_ui
 	pack $w.desc -side top -fill x -padx 5 -pady 5
 
+	set v [exec git --version]
+	append v "\n\n"
+	if {$tcl_patchLevel eq $tk_patchLevel} {
+		append v "Tcl/Tk version $tcl_patchLevel"
+	} else {
+		append v "Tcl version $tcl_patchLevel"
+		append v ", Tk version $tk_patchLevel"
+	}
+
 	label $w.vers \
-		-text [exec git --version] \
+		-text $v \
 		-padx 5 -pady 5 \
 		-justify left \
 		-anchor w \