Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

pkgbase: Create a FreeBSD-dwatch package

While dwatch is useful some users might not want it by default.
Create a package for it.

Differential Revision: https://reviews.freebsd.org/D31796

Introduce dwatch(1) as a tool for making DTrace more useful

Reviewed by: markj, gnn, bdrewery (earlier version)
Relnotes: yes
Sponsored by: Smule, Inc.
Differential Revision: https://reviews.freebsd.org/D10006