build system: prevent endless loop when using dunecontrol

this seems to be a bug in cmake 2.8.10.2: if the user sets the
CMAKE_CXX_COMPILER variable for a build directory where this variable
has already been set, one gets an endless loop. This stings especially
if using the dunecontrol compatibility layer as the compiler flags are
unconditionally set via the CXX_FLAGS environment variable in the
options file. Running duncontrol on a module twice will thus trigger the
infinite loop if some compiler flags are set by the user.

The solution is relatively simple: Delete the CMakeFiles directory
before calling cmake. for the dunecontrol compatibility mode, we do
this in the configure script. For details about the cmake bug, see
http://www.cmake.org/Bug/view.php?id=14119
configure script: also delete the cmake cache

This replicates the autotools behavior and was suggested by Roland
Kaufmann.
Extract common parts of blackoil and incomp. state

Put the identical parts of the simulator state into a base class that
they can be referenced from when adressing the common fields.
configure script: add a stub implementation for the --config-cache argument

so far, it is only a flag which prevents the cache from being
deleted. To warn the user about a potential infinite loop, a warning
is printed if this flag was specified and some compiler or some compiler
flags were set by the user. This idea was proposed by Roland Kaufmann.
include the latest review comments by Roland Kaufmann
Search in build/ sub-dir if only suite root is given

If the package suite was given (e.g. DUNE_ROOT=/blum), then the code
set up the root for each individual package automatically (e.g.
DUNE_COMMON_ROOT=/blum/dune-common), but the path which was then
activated did not get the local build sub-directory (e.g. if we are
building opm-autodiff in /frub/opm-autodiff/build, then the local
build directory is "build/"), and thus this was not appended to the
library search path. The result was that the source was found (because
the root pointed to a valid source tree), but the library was not
(because it is "hidden" in the subdirectory).
Only add build sub-directory if it is actually used

Otherwise the search will cascade down one level too many.
Only add parent directories for actual variants

Otherwise we'll inadvertedly add the root directory and will probably
find the system implementation underneath there.
Merge pull request #430 from andlaus/fix_infinite_configure

build system: prevent endless loop when using dunecontrol
fix syntax error in configure shell script

strangly enough, it seems to work like it was in some circumstances...
Merge pull request #436 from rolk/436_searchdir

Search in build/ sub-dir if only suite root is given
Merge pull request #420 from rolk/420_state

Refactor BlackoilState and TwophaseState to have a common interface for writing
Merge pull request #439 from andlaus/fix_configure_syntax_error

fix syntax error in configure shell script
configure: fix all except one warning produced by shellcheck

thanks to @bska for pointing this tool out!
Merge pull request #440 from andlaus/fix_shellcheck_warnings

configure: fix all except one warning produced by shellcheck