Clean up .travis.yml

- use env: global/matrix sections instead of inline scattered exports
- use official travis env var for SRC directory
- remove travis-ci default installed libhdf5 and packages that depend on them
  (mainly web database stuff like postgresql)
- install hdf5 libs and their dependencies (!) with -t explicitly from the ppa
- add some more debug information about apt-cache package policy
Merge pull request #84 from ax3l/topic/travisCleanup

Clean up .travis.yml
Add new parallel test for zero accesses

 - tests reading/writing with size=0
Add debug output
Remove working tests
Only print on error
Merge branch 'zero-access-dbg' of github.com:ComputationalRadiationPhysics/libSplash into zero-access-dbg

Conflicts:
	tests/Parallel_ZeroAccessTest.cpp