MACRO(CREA_PREVENT_IN_SOURCE_BUILD)
  IF(NOT CREA_ALLOW_IN_SOURCE_BUILD)
    #------------------------------------------------------------------------
    # Building in the source tree is forbidden ! 
    # except if CREA_ALLOW_IN_SOURCE_BUILD is set, 
    # e.g. for packaging with rpmbuild
    IF(PROJECT_BINARY_DIR STREQUAL ${PROJECT_SOURCE_DIR})
      MESSAGE(FATAL_ERROR "Building in the source tree is not allowed !! Quit; remove the file 'CMakeCache.txt' and the folder 'CMakeFiles' and build outside the sources")
    ENDIF(PROJECT_BINARY_DIR STREQUAL ${PROJECT_SOURCE_DIR})
    #------------------------------------------------------------------------
  ENDIF(NOT CREA_ALLOW_IN_SOURCE_BUILD)
ENDMACRO(CREA_PREVENT_IN_SOURCE_BUILD)