Changeset 2612 for code/branches/buildsystem2/cmake/LibraryConfigMinGW.cmake

Rearranged CMake configuration code. I split serveral files in two and moved some code around.
There are no actual code changes!

Details:

• Everything that involves library finding is in LibraryConfig.cmake. It includes other LibraryConfigXXX.cmake files that set specific options for certain platforms or package configurations (like MSVC or MinGW dependency package).
• All build related code is in BuildConfig.cmake. The actual compiler configuration is done in BuildConfigXXX.cmake where XXX can be GCC or MSVC.
• The changes above implied splitting FindOGRE.cmake in two (was going to do it anyway, but rather in a later commit) so that CheckOGREPlugins.cmake is now a separate module.