illumos gate

The current illumos nawk is effectively a fork from the state of Brian Kernighan's nawk in 1989. Sun then restyled the code, and made the occasional independent fix, but they never pulled in upstream changes again. Since the two source bases had diverged significantly, I tried to recreate the history as best as I could, and used that to inform several updates for SmartOS: a mostly non-functional change, a functional change, and one notable breaking change. I then followed up with two other changes (a fix to field splitting, and support for the RT variable). This update for illumos contains all of those changes.

Note that this change only catches nawk(1) up to about late 2018, since I haven't had a chance to evaluate other recent changes yet.