1. ${ROFF} is run in ${.OBJDIR}.
2. the preprocessor prefixes ${SRCDIR}/ to relative pathnames in `.so'
statements.
This is useful when running ${ROFF} in the source directory isn't
convenient.
Added dependencies on ${EXTRA} and ${OBJS}. These are usually for files
that are sourced indirectly. ${OBJS} is for files that are built.
4.4lite has decentalized incomplete dependencies on ${EXTRA} and ${DPADD}.
These were broken by are centralized handling of the roff targets.