Export HAVE_DUNE_ISTL for other modules.

This is e.g. needed in the parallel version of autodiff to
test whether ISTL is there.
Search for MPI support

The build system depends on knowing if MPI is available.  Explicitly
search for MPI to honour that requirement.  Don't rely on ISTL's
transitive searching for the same.
add option to quell dune(-istl) warnings
Added more warnings to suppression list, sorted list.
Change option name and generated header names.
add support for the UG grid library

recently UG has become free software (yay!), so we can now support it
with a good conscience. The CMake module is based on the "UseUG.cmake"
module of dune-grid but it is quite a bit simpler and actually
works. (I cannot see how UseUG.cmake can work without ever including
the ug-config*.cmake files...)

the UG source code is available here:

https://github.com/ugfem/ug
Fix option name to match name in use in conditional.

Also add a useful doc string.
do not add the "-Wl,--as-needed" linker flag in FindSuiteSparse.cmake

because if umfpack is fully linked but some other library is
underlinked, it causes the build to fail. This flag is better dealt
with in the "UseOnlyNeeded.cmake" module...
make the "-Wl,--as-needed" flag optional

as there is not much harm done if it is not used but it may cause the
build to fail if it is present (read: it causes _my_ build to fail),
it defaults to OFF.
Make dune-cornerpoint a suggestion.
Merge pull request #58 from bska/sync-build

Synchronise build system with OPM-Core
move the code away from EclipsGridParser to opm-parser
Merge pull request #59 from andlaus/move_to_opm-parser

move the code away from EclipseGridParser to opm-parser
fix a pretty simple compile issue

This was caused by the new multi-region PVT support in opm-core.
Merge pull request #60 from andlaus/implement_multi-region_pvt_tables

fix a pretty simple compile issue
use the EclipseState instead of the raw deck

this is needed to enable property modifiers...
Merge pull request #61 from andlaus/enable_property_modifiers

use the EclipseState instead of the raw deck
allow the opm-parser test to fail

since the module currently calls the tests for cJSON and boost with
the REQUIRED flag set, cmake aborts completely even if opm-parser is
not REQUIRED. For modules which depend on opm-core that's currently a
non-issue because core has a requirement on parser, but the parser may
be useful for external projects as well, so we play nice.

Also, with this patch the config.h variable HAVE_OPM_PARSER is set...
Findopm-parser.cmake: make sure that the ERT libraries are available

and some other minor cleanups to the module. For me it still works,
but this being the build system, I can't guarantee more...
Findopm-parser.cmake: invoke FindBoost unconditionally

even if boost was found previously, it might still miss a few
libraries. thanks to @akva2 for catching this.