ps: making the libselinux support configurable

ps: making the libselinux support configurable

Previously the libselinux support was present
in the sources, but disabled with a preprocessor
condition (#if 0).
From now the libselinux support can be enabled with
the --enable-libselinux switch available
in the configuration script. That way is more
flexible than local patches modifying the condition
value from 0 to 1.