OpmFind.cmake: prevent multiple calls to the same module in the same run

this prevents to check for the same module more than once in the same
cmake run and should thus speed things up a bit as well as make the
output a bit cleaner. For this I assumed that the ${name}_FOUND cmake
variable does not get cached, which it seems like it does not...
cmake: make sure all calls to message() exhibit a type
OpmFind.cmake: also check for CAPITALIZED found variables

thanks to @rolk for catching this
Added pvt functionality for wetgas
The pvt interface is extended to handle wet-gas systems:
1. rvSat is added as a function in the PVT interface
2. SinglePvtLiveGas computes the pvt values and its derivatives
3. The old rbub variable is changed to rsSat for clearity
4. The new interface is tested in test_blackoilfluid with data from
liveoil.DATA and wetgas.DATA
Initialization using the RV keyword
The initial Rv value is specified using the RV keyword in the Parser.
The Rv values are used in the computation of the initial surface
volumes.
Change the extrapolation in the livegas pvts
The special extrapolation for pressure values above
the maximum table value is removed to sync with Mrst
Phase pressure is used for surface volumes calculations
Merge pull request #450 from andlaus/add_message_type

cmake: make sure all calls to message() exhibit a type
Fixing comments
The comment now currently say 1/Bg
Merge pull request #462 from totto82/wetgas

Added pvt functionality for wetgas
Merge pull request #448 from andlaus/prevent_multiple_package_detections

OpmFind.cmake: prevent multiple calls to the same module in the same run
Create aliases for probed variables

Headers from other libraries (notably DUNE) require definitions of
other variables than our probe process set (e.g. HAVE_UMFPACK instead
of HAVE_SUITESPARSE_UMFPACK_H). This module sets those aliases for
compatibility.
Declare a need to know if UMFPACK is available

Note that the variable HAVE_UMFPACK is not set by FindSuiteSparse,
but by OpmAliases.
Declare a need to know if BOOST is available

Note that the variable HAVE_DUNE_BOOST is not set by FindBoost,
but by OpmAliases.
Merge pull request #475 from rolk/475_dunedef

Alias probed CMake variables to names that DUNE require
Merge remote-tracking branch 'upstream/master' into opm-parser-integrate