Followup to bug 579178 part B (packaging) - only create the mochitest distribution bundle directory if it doesn't already exist

testing/mochitest/runtests.py.in

@@ -692,7 +692,8 @@ overlay chrome://browser/content/browser.xul chrome://mochikit/content/browser-t
   def installChromeFile(self, filename, options):
     (path, leaf) = os.path.split(options.app)
     manifestdir = os.path.join(path, "distribution", "bundles", "mochitest")
-    os.makedirs(manifestdir)
+    if not os.path.exists(manifestdir):
+      os.makedirs(manifestdir)
     manifest = os.path.join(manifestdir, "chrome.manifest")
     shutil.copy(filename, manifest)
     return manifest