Make print/ghostscript9-agpl-base the default Ghostscript port. Upstream
changed the license to the AGPL 3 in version 9.07 so print/ghostscript9-base
is stuck at 9.06 which is almost 4 years old now.

Fix the logic in Uses/ghostscript.mk so "agpl" is treated as a real version
on its own instead of as a variant of other versions.

Fix print/ghostscript9-agpl-base to install eps2write.

Update math/asymptote to 2.37 to support newer Ghostscript.

PR: 208159
Exp-run by: antoine
Approved by: portmgr (antoine)