unset( SKIP_EXTERNALS CACHE ) # must remove so as not to trap user into a never ending failure
unset( PACK_EXTERNALS CACHE )
message( FATAL_ERROR "ERROR: PACK_EXTERNALS can be set only if SKIP_EXTERNALS is unset (=0, or not supplied on command line)" )
unset( SKIP_EXTERNALS CACHE ) # must remove so as not to trap user into a never ending failure
unset( PACK_EXTERNALS CACHE )
message( FATAL_ERROR "ERROR: PACK_EXTERNALS can be set only if SKIP_EXTERNALS is unset (=0, or not supplied on command line)" )