git-gui: Update known branches during rescan.

If the user has created (or deleted) a branch through an external tool,
and uses Rescan, they probably are trying to make git-gui update to show
their newly created branch.

So now we load all known heads and update the branch menu during any
rescan operation, just in-case the set of known branches was modified.

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

git-gui.sh

@@ -400,7 +400,7 @@ proc rescan {after {honor_trustmtime 1}} {
 	global HEAD PARENT MERGE_HEAD commit_type
 	global ui_index ui_workdir ui_status_value ui_comm
 	global rescan_active file_states
-	global repo_config
+	global repo_config single_commit
 
 	if {$rescan_active > 0 || ![lock_index read]} return
 
@@ -427,6 +427,11 @@ proc rescan {after {honor_trustmtime 1}} {
 		$ui_comm edit modified false
 	}
 
+	if {!$single_commit} {
+		load_all_heads
+		populate_branch_menu
+	}
+
 	if {$honor_trustmtime && $repo_config(gui.trustmtime) eq {true}} {
 		rescan_stage2 {} $after
 	} else {