Correct mixup between option and cache variables

Options are boolean flags that are stored... in the cache, whereas
cache variables are also stored in the cache, but can have a variety
of types (including booleans). It was possible to confuse the two,
because if you set it as a variable on the command line, it will
override both.
Allow more variety in unit test program file names

They can now be called test_*.cpp or *_test.cpp
Specify source directory at the highest level

Some projects also have side directories for utilities etc.
Make project file easier to customize

Note where opm-core specific parts are, and put dependency listing to
the top where it is more noticable.
Allow --without as an alias to --disable

This gives a symmetry to --with-xxx options
Rearrange options in order of need

Boost is very little likely to be removed from the list of dependencies;
we rather want a continuous block to remove when customizing.
Replace hardcoded opm-core name with variable
Reorder dependency list

Should still be queried in topological order
Distinguish between AGMG and opm-core specific

The AGMG parts may be reusable in other projects
Use generic names in other files also

Reduce the number of files that must be customized when starting new
projects.
Merge pull request #160 from akva2/redhat_packaging

added: spec file for redhat packaging
Use generic name for configure wrapper also
Merge pull request #149 from rolk/149_projstruct

Harmonize project structure to maximize build code reuse
Merge pull request #154 from akva2/debian_packaging

added:  debian packaging control files
Merge pull request #162 from bska/release-cleanup

Release cleanup
Merge pull request #158 from rolk/158_yum_apel

Describe how to get extra packages from OPM repo
Remove GNUmakefile, document cmake building.

The README now suggests using nice and make -j for multicore machines.
Expand instructions for separate build directory

This, hopefully, makes the steps a bit more clear by introducing an
explicit layout example to which the command sequences can relate.
Merge pull request #2 from bska/remove-gnumakefile

Expand instructions for separate build directory
Handle all DUNE and OPM modules the same way

dunecontrol will specify --with-* for each and every module that is
listed as a dependency in dune.module; there is no difference between
them because they all share the same code :-)