Using logog logging within class Gmsh2GeoIO.
Using logog logging within class MeshIO.
Updated copyright to 2013.
Using logog logging in file OGSIOVer4.cpp.
Using logog logging within class PetrelInterface.
Updated copyright to 2013.
Using logog logging in classes GMSHInterface and GMSHAdaptiveMeshDensity.
Removed compile time dependencies deploying forward declaration in class GMSHAdaptiveMeshDensity.
Using logog logging within class GMSInterface.
Using logog logging in file readMeshFromFile.cpp.
Using logog logging in class SHPInterface and refomatting source code.
Removed method zLibDataCompressor::GetMaximumCompressionSpace() since it has no implementation.
Using logog logging within class zLibDataCompressor.
Using logog logging within class XmlCndInterface.
Using logog logging in class XmlLutReader.
Using logog logging within class XMLInterface.
Renamed CMake option OGS_DONT_USE_OPTIONAL_SUBMODULES to OGS_USE_OPTIONAL_SUBMODULES.

Searching for optional submodules has to be actively enabled by this
option. This prevents unexpected CMake errors when developers checked
out the submodules without their knowledge (as it happens e.g. with
the Windows GitHub app).
Using logog logging within class XmlGspInterface.
Using logog logging within class XmlGmlInterface.
Using logog logging in class XmlStnInterface.