rc: tab character issue

[mgood]

Tried typing cat h<tab>. The tab moved the cursor forward multiple spaces. When I pressed backspace it deleted a single space at a time. But then the cursor stops, leaving the rc% cat h prompt. So it seems like there's a display issue with what is displayed vs internal buffer.

[progrium]

This could actually be a terminal issue. Taking the Plan 9 approach to pty with our #term devices, we don't implement line discipline there like one might expect. Instead, I've started implementing that behavior "toward the edge" in <wanix-term>. But it's very incomplete. If you wanna take a stab at implementing the rest, that would be cool. If not, maybe come up with a test case showing at least that that is the issue (or part of the issue), and maybe what more specifically rc might be doing wrong.