code: function _loadSHA(path, callback) {
          var result = new $.Deferred();
  
          if (brackets.inBrowser) {
              result.reject();
          } else {
              // HEAD contains a SHA in detached-head mode; otherwise it contains a relative path
              // to a file in /refs which in turn contains the SHA
              var file = FileSystem.getFileForPath(path);
              FileUtils.readAsText(file).done(function (text) {
                  if (text.indexOf("ref: ") === 0) {
                      // e.g. "ref: refs/heads/branchname"
                      var basePath    = path.substr(0, path.lastIndexOf("/")),
                          refRelPath  = text.substr(5).trim(),
                          branch      = text.substr(16).trim();
  
                      _loadSHA(basePath + "/" + refRelPath, callback).done(function (data) {
                          result.resolve({ branch: branch, sha: data.sha.trim() });
                      }).fail(function () {
                          result.resolve({ branch: branch });
                      });
                  } else {
                      result.resolve({ sha: text });
                  }
              }).fail(function () {
                  result.reject();
              });
          }
  
          return result.promise();
      }
docs: Loads a SHA from Git metadata file. If the file contains a symbolic ref name, follows the ref
  and loads the SHA from that file in turn.