Unfortunately, alberta headers globally defines TEST, which leads to tons
of compiler warnings. Te clean solution is to not let gtest define TEST.
This unfortunately requires us to write GTEST_TEST instead of TEST.

# Conflicts:
#	.gitignore
#	.travis.yml
#	dune.module

This did not compile for me with clang 3.8.1-12~bpo8+1 using gcc
4.9.2-10 stdlib. Any objections against this change, @dune-xt-common-devs?
Was there any reason to use int instead of double in the first place?

Previously, TBB_INCLUDE_DIR was ignored, although documented as possible
hint to where the tbb include might be. No it is respected, hopefully
without breaking findidn of system installation ...

The old behavior only added `-lboost_system` but did not add
`-L/path/to/boost/lib`.

Previously, TBB_INCLUDE_DIR was ignored, although documented as possible
hint to where the tbb include might be. No it is respected, hopefully
without breaking findidn of system installation ...

The old behavior only added `-lboost_system` but did not add
`-L/path/to/boost/lib`.

This reverts commit 2d4ecdc8.

This reverts commit 0ba1776a.