Add new variable USE_PERL5.  It is similar to USE_GMAKE, except that it also sets RUN_DEPENDS (USE_GMAKE is BUILD_DEPENDS only).
Add new variable USE_PERL5.  It is similar to USE_GMAKE, except that
it also sets RUN_DEPENDS (USE_GMAKE is BUILD_DEPENDS only).

The (immediate) purpose of this is to avoid having to change 70
zillion ports when the version of perl changes.  Also, when perl5 is
pulled into -current, this will become a no-op in -current's
bsd.port.mk.

Reviewed by:	jfitz

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