fix dayplot in case of problems during event download
docs: dont render image plots as pdf to avoid huge files, adapt Makefile
accordingly, sphinx' latexpdf uses pdf files so replace file extensions in
built tex output files before pdflatex, slightly higher dpi for png
images so tutorial pdf still looks good
docs: add downloadable link to Tutorial pdf (has to be built with "make
latexpdf" independently)

build has to be done like this for this to work:
 - make html
 - make latexpdf
 - make html
docs: adding docs-buildbot script
docs: add links to introduction ipy notebooks on tutorial page
Merge pull request #793 from megies/fix_doc_building

Fix doc building
Merge branch 'releases'

Conflicts:
	obspy/imaging/waveform.py
try to fix travis (see https://github.com/travis-ci/travis-ci/issues/2219#issuecomment-41804942)
Merge branch 'releases'

Conflicts:
	.travis.yml
safer plot directive use (try to fix a broken plot in docs-buildbot master branch gallery)
deb packaging: include python-dev in build-depends
Merge branch 'releases'
lib: central helper funtion for importing CDLLs
lib: use central helper function to import CDLLS
lib: fix appending extension suffix to CDLL names
fix signal test suite
lib: unify windows libtau import
Ignore __pycache__ dirs
add future dependency to test reports
(1) removes deprecated st.taper() call from core tests
(2) fixes a strange behaviour for huge slice index on an numpy.array
(3) PEP8