audio/pulseaudio: convert JACK option to a package

[ivy]

Summary

Added a new 'jack' subpackage to audio/pulseaudio, which contains the JACK
input/output plugins.

This should be a fairly trivial and straightforward example of a subpackage,
since it's just a few loadable modules (.so files) with a dependency on
audio/jack.

Test Plan

Built the new packages, installed them, tried to play audio in
multimedia/musikcube, audio worked.

[arrowd]

audio/pulseaudio/Makefile

18

Why ?= ?

20

This is default and shouldn't be needed.

[ivy]

audio/pulseaudio/Makefile

18

i couldn't find any documentation for subpackages, so i based this on https://reviews.freebsd.org/D43445 (appstream) which used ?=. i can change this if it's wrong.

20

okay, i'll removed that.

[ivy]

change SUBPACKAGES?= to =, removed DESCR.jack

[ivy]

closing this since there hasn't been any progress on the subpackages situation and i'm no longer in a position to easily test it.