Check for cegui-0 and CEGUIBase-0 in priority, since these are the upstream names for CEGUI 0.8.x
This prevents inadvertly building against CEGUI 0.7.x if it is installed on the system.
The unused FindCEGUIOGRE.cmake script has been removed, since we search for CEGUIOgre in the FindCEGUI.cmake script.
Set the proper C++11 flag in CMAKE_CXX_FLAGS for MinGW and UNIX
Was tested with GCC 4.9.2 on Linux, but I read the flag defined for Unix should work on Mac with clang.
Drop the hardcoded optimisation flags; those can be defined passing CMAKE_CXX_FLAGS as an argument to cmake or cmake-gui (the C++11 flag is appended to the user-defined flags)