use python 2.7 runtime
replace use of use_library with libraries stanza
add workaround to prevent DJANGO_SETTINGS_MODULE errors
define TEMPLATE_DIRS in django settings

This allows us to do away with the _swap_settings hack.
no need for fix_path.fix_sys_path()

Issue #772 [1] seems to have been fixed.

[1] http://code.google.com/p/googleappengine/issues/detail?id=772
let GAE run our WSGI config
static: force Content-Type to be a str

db.StringProperty seems to be always returning unicode, even if input
was a bytestring. When run as a WSGI app, a unicode header caused the
handler to crash.
Merge branch 'rc/py27' into rc/master