Feature/dune exception derived from std exception

I almost missed Christian's last commit. It was poor luck  that I had a look into the commit history before replacing the old remote URL by the new, Gitlab-based one. I manually transferred his commit and saved myself the work of programming what Christian already did.

See merge request !2

Previously, the script that splits the in-module documentation
into parts exited with cryptic error messages that gave no hint
on where the typo happened. It now prints the offending line.

In dune-testtools we built a sphinx cmake documentation which is customized
quite a bit. With the core functionality being in dune-common, it is hard
to maintain it twice. I have therefore added some options to the dune-common
doc infrastructure, that are beneficial downstream.

You can now:
* provide custom rst sources
* provide a custom sphinx-build conf file
* limit the documentation to the current module, instead of adding all requirements automatically

The defaults of all those parameters result in an unchanged behaviour
(compared to before this commit).

As talked about on the developer meeting, a configure
switch should allow to build the tests during make all.
You can either set it through your opts file or activate
it on a per module level. If not active, you have to run

make build_tests && make test

to run the test suite.

We should always use the DUNE_ prefix for our cmake
variables, to avoid scoping clashes and to stay consistent.

Sorry for not doing this immediately, it was an oversight.

This way, the docs get much more readable.

This is a follow-up to commits
7d118c6f and
e488a7c1.

The warning was added before FS#493 and the related FS#491
were resolved. Probably it was just forgotten to remove the
warning.
I double checked with GCC 5 and -O3. Works for me.

The file has been deleted in 152817d2.

Probably an error caused during merging.

Implements the dune_add_test mechanism and
applies it to all the dune-common tests.

Conflicts:
	dune/common/test/CMakeLists.txt

It allows ctest to correctly schedule parallel tests
even though running through ctest -j.

This enables users to have several build directories like
build-clang, build-gcc5, build-debug, and still get all
of them ignored.

A list of numbers may be given and the test is executed with all
those processor numbers, unless the user variable DUNE_MAX_TEST_CORES
is exceeded. In sequential builds, tests with a number higher than 1
are discarded.

Nothing needs to be included with proper C++11 compilers.

Old feature support macros which were tested until 2.4, kept around
for one more release. As these are now always supported due to the
new compiler requirements, they are directly defined without an
explicit test.

Conflicts:
	cmake/modules/CMakeLists.txt
	cmake/scripts/CMakeLists.txt

It is outdated.