Update py-jinja2 to 2.7.

Version 2.7
-----------
(codename Translation, released on May 20th 2013)

- Choice and prefix loaders now dispatch source and template lookup
  separately in order to work in combination with module loaders as
  advertised.
- Fixed filesizeformat.
- Added a non-silent option for babel extraction.
- Added `urlencode` filter that automatically quotes values for
  URL safe usage with utf-8 as only supported encoding.  If applications
  want to change this encoding they can override the filter.
- Added `keep-trailing-newline` configuration to environments and
  templates to optionally preserve the final trailing newline.
- Accessing `last` on the loop context no longer causes the iterator
  to be consumed into a list.
- Python requirement changed: 2.6, 2.7 or >= 3.3 are required now,
  supported by same source code, using the "six" compatibility library.
- Allow `contextfunction` and other decorators to be applied to `__call__`.
- Added support for changing from newline to different signs in the `wordwrap`
  filter.
- Added support for ignoring memcache errors silently.
- Added support for keeping the trailing newline in templates.
- Added finer grained support for stripping whitespace on the left side
  of blocks.
- Added `map`, `select`, `reject`, `selectattr` and `rejectattr`
  filters.
- Added support for `loop.depth` to figure out how deep inside a recursive
  loop the code is.
- Disabled py_compile for pypy and python 3.


(kleink)