Eliminated cmake warning for case when python is not found.

CMakeLists.txt

@@ -627,7 +627,7 @@ if(WIN32)
     set(PYTHON_PACKAGES_PATH "${PYTHON_PATH}/Lib/site-packages")
 endif()
 
-IF (${PYTHON_VERSION_MAJOR_MINOR} VERSION_GREATER 2.5)
+IF ("${PYTHON_VERSION_MAJOR_MINOR}" VERSION_GREATER 2.5)
     SET(PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE} -B)
 ENDIF()