Two new FDSN tests.

Tests the created URLS. Fixing some minor bugs along the
way.
Adjusting test cases once again...
Custom per-service endpoints can now be specified.

Also added a short test.
changelog
fdsn: add possibility to deactivate single services in client (+test)
Added test for actually downloading things with custom mappings.
PEP8
fdsn tests: only initialize clients once
Merge pull request #754 from krischer/fdsn_enhancements

Feature request: override capabilty for specific FDSN web service locations
scale down docstring example plot in tf_misfit.py

@martinvandriel, this example plot in the docs consumed 2.5 GB of
memory, making sphinx docs building fail erratically for me (and running
my RAM full several times in the process). Even with these reduced
settings it takes 300 MB, maybe there is something wrong in there?
..this memory consumption seems a bit excessive.
Merge remote-tracking branch 'upstream/releases'

Conflicts:
	obspy/fdsn/client.py
	obspy/fdsn/tests/test_client.py
Merge branch 'releases'