Revise the manpage to a certain extent, mostly with respect to make's processing of top-level and included makefiles.  Point out at make.conf(5) and __MAKE_CONF when telling about sys.mk.
Revise the manpage to a certain extent, mostly with respect to
make's processing of top-level and included makefiles.  Point
out at make.conf(5) and __MAKE_CONF when telling about sys.mk.

Reviewed by:	ru

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase