fdsn: tests for client with authentication
fdsn: add authentication
fdsn: fix/adjust (doc)tests

@krischer: py.test is not checking doctests by default
fdsn: fix Client.help()
Merge pull request #649 from obspy/fdsn_auth

fdsn client with authentication
fdsn: some minor changes and refactoring

 - new method to fetch the actual, full version numbers of webservices
 - insert method numbers into help() message and Client.__str__()
 - refactoring
 - adapt tests for version number in strings
fix tests
updating python coverage link to coverall

closes #648
correct syntax, see #642

to my knowledge no "normal arguments" are allowed in python after a keyword
argument was already specified.