Added extension ordering, this fixes #376.

--HG--
branch : trunk
diff --git a/jinja2/parser.py b/jinja2/parser.py
index 1f5e12a..9814c93 100644
--- a/jinja2/parser.py
+++ b/jinja2/parser.py
@@ -34,7 +34,7 @@
         self.filename = filename
         self.closed = False
         self.extensions = {}
-        for extension in environment.extensions.itervalues():
+        for extension in environment.iter_extensions():
             for tag in extension.tags:
                 self.extensions[tag] = extension.parse
         self._last_identifier = 0