cylc/cylc#415: fix localhost background submit.

localhost job submit: add bracket around the command to prevent
incorrect pipings.
In UTC mode, set environment variable TZ=UTC.
Merge pull request #418 from matthewrmshin/utc+

In UTC mode, set environment variable TZ=UTC.
Merge pull request #417 from matthewrmshin/415.fix.job-submit-local

Fix localhost background submit
Officially drop Python 2.4 support, which is already broken.

Closes #389. This commit just:
 * updates the user guide "requirements" section;
 * removes a few back-ports of the python 2.5 'any' statement
Merge pull request #420 from hjoliver/389.drop-python-2.4

Officially drop Python 2.4 support, which is already broken.