Removing Python 2.5 from the Travis config since Jinja2 no longer supports it

The latest versions of Jinja2 no longer support Python 2.5 [[1], [2],
[3]]. Since Jinja2 is an integral part of Flask, this would also mean
that Flask no longer supports versions of Python prior to 2.6. Since
Flask no longer supports versions of Python prior to 2.6, plugins for
Flask do not need to support them either and so, the 2.5 Travis test
can be removed.

[1]: https://github.com/mitsuhiko/jinja2/pull/185#issuecomment-18098870
[2]: https://github.com/mitsuhiko/jinja2/commit/b89d1a8fe3fcbd73a8f4cebd4358eadebc2d8a9d
[3]: https://github.com/mitsuhiko/jinja2/commit/8bdc65d9e57d5c0da329bb88127d977bd58002e5
support SQL-standard date/datetime functions

This allows setting date and datetime type fields to the values `CURRENT_DATE`, `CURRENT_TIMESTAMP`, and `LOCALTIMESTAMP` from the API, and translates that into SQL expressions that get evaluated by the database.

This allows client-side code to set a date or timestamp to current as seen by the server, in case the client computer's clock is incorrect.
Revert "Adds a wrapper around abort function to add JSON Content-Type."

This reverts commit 8aacd39d91777f10153424e47cbb5d1c2833491a.

Conflicts:
	tests/__init__.py
	tests/test_exceptions.py
allow disabling deep results per-request

originally by @johaness
allow fine grained control of relations included in output
bump to 1.current-upstream-version