Add listStatuses repo endpoint

Author: pik

github.js

@@ -329,6 +329,16 @@
             _request('DELETE', repoPath, options, cb);
          };
 
+         this.listStatuses = function(sha, cb) {
+            _request('GET', repoPath + '/statuses/' + sha, null, function(err, heads, xhr) {
+               if (err) {
+                  return cb(err);
+               }
+
+               cb(null, heads, xhr);
+            })
+         };
+
          // Uses the cache if branch has not been changed
          // -------