git-gui: Show the git-gui library path in 'About git-gui'

Because we now try to automatically guess the library directory
in certain installations users may wonder where git-gui is getting
its supporting files from.  We now display this location in our
About dialog, and we also include the location we are getting our
Git executables from.

Unfortunately users cannot use this 'About git-gui' dialog to
troubleshoot library loading problems; the dialog is defined by
code that exists in the library directory, creating a catch-22.

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

git-gui.sh

@@ -59,7 +59,7 @@ if {$idx ne {}} {
 } else {
 	set auto_path [concat [list $oguilib] $auto_path]
 }
-unset -nocomplain oguilib oguirel idx fd
+unset -nocomplain oguirel idx fd
 
 if {![catch {set _verbose $env(GITGUI_VERBOSE)}]} {
 	unset _verbose

lib/option.tcl

@@ -52,7 +52,7 @@ proc save_config {} {
 }
 
 proc do_about {} {
-	global appvers copyright
+	global appvers copyright oguilib
 	global tcl_patchLevel tk_patchLevel
 
 	set w .about_dialog
@@ -91,6 +91,10 @@ $copyright" \
 		append v ", Tk version $tk_patchLevel"
 	}
 
+	set d {}
+	append d "git exec dir: [gitexec]\n"
+	append d "git-gui lib: $oguilib"
+
 	label $w.vers \
 		-text $v \
 		-padx 5 -pady 5 \
@@ -100,6 +104,15 @@ $copyright" \
 		-relief solid
 	pack $w.vers -side top -fill x -padx 5 -pady 5
 
+	label $w.dirs \
+		-text $d \
+		-padx 5 -pady 5 \
+		-justify left \
+		-anchor w \
+		-borderwidth 1 \
+		-relief solid
+	pack $w.dirs -side top -fill x -padx 5 -pady 5
+
 	menu $w.ctxm -tearoff 0
 	$w.ctxm add command \
 		-label {Copy} \