The directory is different on Linux Mint 13. This needs to be in the CMakeLists.txt
if(UNIX)
if(EXISTS "/usr/share/OGRE/cmake")
set(CMAKE_MODULE_PATH "/usr/share/OGRE/cmake/modules/;${CMAKE_MODULE_PATH}")
set(OGRE_SAMPLES_INCLUDEPATH "/usr/share/OGRE-1.7.4/Samples/Common/inc