Log Message:
jack: Update to 1.9.19

This switches us to jack2, the latest rewrite of the JACK audio
server, with support for Solaris, Linux, macOS, and NetBSD (support
for NetBSD added by me in a series of patches...)

My primary motivation for this update is to avoid jack1's unpleasant
abuse of unix domain sockets such that it no longer works in NetBSD
9.99.x (see PR kern/56113)