List files that are needed to build the library

This list will be picked up by the modules at a later commit.
Specify source files explicitly rather than with glob
Allow uppercase alternatives for package location vars
Fix bug with whitespace at end of env.var.
Don't add anything if no precompiled header is specified
Only regenerate config var file if actually changed
Remove make execution wrapper
Conditionally disable example if compiler is not C++11
Find OpenMP in a reusable way
Use OpenMP in this project

The source code have #pragma omp, so we should enable this from the
command line. (But why isn't it inherited from opm-core?)
Merge pull request #20 from rolk/020_cmakeupd

Update CMake scripts to commit 11bf7bf3 from opm-core
Update CMake scipts to commit e75d69ef from opm-core
Merge pull request #22 from rolk/022_cmakeupd

Update CMake scipts to commit e75d69ef from opm-core
Handle ERT not found condition gracefully

If the files for ERT is not found, then the find module cheats and
indicates that it didn't compile either (since there are some later
tests for HAVE_ERT).

However, erraneously, it gave this variable the value 0, which tests
for false in the CMake code but not in the #ifdef checks in the C++
code. This error is cancelled in opm-core by the fact that it didn't
store it as a cache variable, but resurfaced in opm-polymer when it
probes the second time (as both opm-core as a dependency and
opm-polymer itself declare a dependency on ERT).

It is now stored in a way that should be satisfactory to both
projects.
Enable dunecontrol to use a build tree as module dir

dunecontrol looks for a dune.module to determine whether a directory
contains a module or not. By copying this file to the build tree, we
can use (out-of-source!) build trees in dunecontrol too.
Only warn for unknown --enable/--with options

Follow the guidelines in
<http://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.69/
html_node/Option-Checking.html#Option-Checking>
and print a *warning* if there is an unknown --enable-* or --with-*
option, error otherwise. --disable-option-checking does not turn off the
errors, but silences the warnings.
Allow variables and options in any order

Traditionally, options are put before any other command-line arguments.
However, dunecontrol puts variable assignment before options, like env,
and this confuses getopt.

This variant (based on a suggestion by Andreas Lauser) collects the
variables into an array at the same time as the options are processed.
Only make actual directory names canonical

If the directory that is specified does not exist, then keep the path
as entered, which makes for better error messages later.

We cannot print an warning on a non-existent name, because it may be
target directories that are specified, or perhaps logical options
(like --with-mpi=yes)
Determine that ERT is not found, faster

Instead of checking every pre-requisite and then determine if the
library is functional, quickly check if the library directories are
present, and if not bail out. The most common reason that ERT is
not usuable, is that it is installed, not that something else is
missing!
Bugfix wrong variable used

But since it added the option anyway, this was hard to catch (unless
one was trying to set both options at the same time)