SCM: Git clone performance

Via:
- http://stackoverflow.com/questions/1778088/how-to-clone-a-single-branch-in-git
- http://stackoverflow.com/questions/6941889/is-git-clone-depth-1-shallow-clone-more-useful-than-it-makes-out
- http://git-scm.com/docs/git-clone

Mage/Task/BuiltIn/Scm/CloneTask.php

@@ -64,16 +64,12 @@ class CloneTask extends AbstractTask
         $this->runCommandLocal('mkdir -p ' . $this->source['temporal']);
         switch ($this->source['type']) {
             case 'git':
-                // Clone Repo
+                // Fast clone Repo form Branch
                 $command = 'cd ' . $this->source['temporal'] . ' ; '
-                         . 'git clone ' . $this->source['repository'] . ' . ';
+                    . 'git clone --depth 1 -q -b ' . $this->source['from']
+                    . ' ' . $this->source['repository'] . ' . ';
                 $result = $this->runCommandLocal($command);
 
-                // Checkout Branch
-                $command = 'cd ' . $this->source['temporal'] . ' ; '
-                         . 'git checkout ' . $this->source['from'];
-                $result = $result && $this->runCommandLocal($command);
-
                 $this->getConfig()->setFrom($this->source['temporal']);
                 break;