git-gui: Delete branches with 'git branch -D' to clear config

If we are deleting a local branch from refs/heads/ we need to
make sure any associated configuration stored in .git/config is
also removed (such as branch.$name.remote and branch.$name.merge).
The easiest way to do this is to use git-branch as that automatically
will look for and delete configuration keys as necessary.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

lib/branch_delete.tcl

@@ -127,7 +127,7 @@ method _delete {} {
 	foreach i $to_delete {
 		set b [lindex $i 0]
 		set o [lindex $i 1]
-		if {[catch {git update-ref -d "refs/heads/$b" $o} err]} {
+		if {[catch {git branch -D $b} err]} {
 			append failed " - $b: $err\n"
 		}
 	}