moved concat to utils, fixed a few docstrings, fixed memory leak in _speedups.escape

--HG--
branch : trunk
diff --git a/jinja2/nodes.py b/jinja2/nodes.py
index d0372e8..83d7573 100644
--- a/jinja2/nodes.py
+++ b/jinja2/nodes.py
@@ -13,10 +13,10 @@
     :license: BSD, see LICENSE for more details.
 """
 import operator
+from copy import copy
 from types import FunctionType
 from itertools import chain, izip
 from collections import deque
-from copy import copy
 from jinja2.utils import Markup