fix the test for the quadmath library

Seems like I forgot to include the "CheckCSourceCompiles" macro before
using it. Since it worked for me before, I'm wondering what made this
happen. Anyway, it should now work correctly in all cases.
cmake: do not quote variables for config.h anymore

v2: incorporate Roland's nitpicks (I hope)
v3: It was decided that it's better to change the default behavior
v4: make sure the CMake syntax is correct even if the value of the
    variable contains spaces (if it contains double quotes it's a
    different matter, but that's pretty much a corner case, IMHO)
v5: properly escape backslash and double quote characters in the cmake
    syntax
avoid to make ALUGRID_PARALLEL_FOUND a list

because -- at least on one of my systems -- a list evaluates to false,
even if all entries are true...
cmake: fix the SuperLU test

for me, it was completely broken. (it worked fine if you did not want
to use it, though.) Now it (hopefully) follows the standard OPM
variable naming conventions, allows to use the internal SuperLU BLAS
library, and works fine if superLU is not installed on a system-wide
basis.

v2: cache the POST_2005 variable to make writing it to config.h more
    reliable (on my kubuntu 13.04 system it did not work without it)
v3: re-add a proper "post 2005" check from newer versions of the dune tests
Merge pull request #329 from andlaus/unquoted_config_vars

cmake: support defining unquoted variables for config.h
add opm-material to the eWoms prerequisites

this is needed by the imminent switch of eWoms to the OPM build
system.
Merge pull request #343 from andlaus/ewoms_add_opm_material

add opm-material to the eWoms prerequisites
Merge pull request #341 from rolk/341_known

Mark known feature variables as used
Merge pull request #339 from andlaus/alugrid_parallel_found_no_list

avoid to make ALUGRID_PARALLEL_FOUND a list
Merge pull request #342 from rolk/342_signals

Provide event mechanism using C++11 instead of Boost::Signals
Merge pull request #340 from rolk/340_suitesparse

Remove subdirectory from SuiteSparse include
Merge pull request #334 from rolk/334_macver

Support configuration on MacOS X using Apple toolchain
Merge pull request #346 from andlaus/fix_superlu_and_quadmath

Fix superlu and quadmath
Merge pull request #335 from rolk/335_multiver

Support multi-versioned installation
Allow build tree of SuiteSparse to be used as root

With this changeset, the build tree of SuiteSparse can be used as the
root; the package does not have to be installed.