Correct Stream.plot documentation on defaults.
Allow setting tick_format for st.plot(type='relative').
Add a reference time for relative Stream plots.

This can be specified with the 'reftime' argument, so the x-axis will be
relative to it, instead of the start time that's plotted.
Add test images for relative Stream.plot.
Merge pull request #766 from QuLogic/relative-plot-reftime

Reference time for relative plots
mock library should be optional only

was always imported, thx to QuLogic, see #732.
add util funtion to cleanse a filename for a python module
use conforming names for library names
avoid dangerous code duplication runtime/build time

comes at the cost of making sure to have no "from obspy .." imports in
the files used at installation time (currently version.py and misc.py in
core.util)
add a basic test to check files used at install time for obspy imports
fix cygwin support for mseed

will be fixed upstream in libmseed for future updates of libmseed, but
this will fix cygwin installation in the meantime until we pull in a
libmseed update.
changelog
event: ease up subclassing

use `self.__class__` instead of explicit class name
Merge remote-tracking branch 'upstream/master' into quakeml_namespaces