Add support for a .gclient_ignore which tells gclient to ignore versioning of...

gclient.py

Index: gclient.py
===================================================================
--- gclient.py	(revision 17798)
+++ gclient.py	(working copy)
@@ -758,6 +758,13 @@
       print("________ found .git directory; skipping %s" % self.relpath)
       return
 
+    # Also skip any diretories maked to be ignored explicitly with
+    # .gclient_ignore.
+    ignore_path = os.path.join(self._root_dir, self.relpath, '.gclient_ignore')
+    if os.path.exists(ignore_path):
+      print("________ found .gclient_ignore; skipping %s" % self.relpath)
+      return
+
     if args:
       raise Error("Unsupported argument(s): %s" % ",".join(args))