git-gui: Refactor reponame computation.

We use reponame in a number of locations, and every time its always the
same value.  Instead of computing this multiple times with code that was
copied and pasted around we can compute it once immediately after the
global gitdir has been computed and set.

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

git-gui.sh

@@ -239,6 +239,9 @@ if {[catch {cd [file dirname $gitdir]} err]} {
 	error_popup "No working directory [file dirname $gitdir]:\n\n$err"
 	exit 1
 }
+set reponame [lindex [file split \
+	[file normalize [file dirname $gitdir]]] \
+	end]
 
 set single_commit 0
 if {$appname eq {git-citool}} {
@@ -2417,7 +2420,7 @@ proc do_include_all {} {
 }
 
 proc revert_helper {txt paths} {
-	global gitdir appname
+	global gitdir appname reponame
 	global file_states current_diff
 
 	if {![lock_index begin-update]} return
@@ -2450,10 +2453,6 @@ proc revert_helper {txt paths} {
 		set s "these $n files"
 	}
 
-	set reponame [lindex [file split \
-		[file normalize [file dirname $gitdir]]] \
-		end]
-
 	set reply [tk_dialog \
 		.confirm_revert \
 		"$appname ($reponame)" \
@@ -2599,7 +2598,7 @@ $copyright" \
 }
 
 proc do_options {} {
-	global appname gitdir font_descs
+	global appname gitdir reponame font_descs
 	global repo_config global_config
 	global repo_config_new global_config_new
 
@@ -2618,9 +2617,6 @@ proc do_options {} {
 	foreach name [array names global_config] {
 		set global_config_new($name) $global_config($name)
 	}
-	set reponame [lindex [file split \
-		[file normalize [file dirname $gitdir]]] \
-		end]
 
 	set w .options_editor
 	toplevel $w
@@ -2756,11 +2752,7 @@ proc do_save_config {w} {
 }
 
 proc do_windows_shortcut {} {
-	global gitdir appname argv0
+	global gitdir appname reponame argv0
-
-	set reponame [lindex [file split \
-		[file normalize [file dirname $gitdir]]] \
-		end]
 
 	if {[catch {
 		set desktop [exec cygpath \
@@ -2806,11 +2798,7 @@ proc do_windows_shortcut {} {
 }
 
 proc do_macosx_app {} {
-	global gitdir appname argv0 env
+	global gitdir appname reponame argv0 env
-
-	set reponame [lindex [file split \
-		[file normalize [file dirname $gitdir]]] \
-		end]
 
 	set fn [tk_getSaveFile \
 		-parent . \