Fix vttest 2.2 / TBC 2
vttest
-> 2
-> 2nd screen is broken. Presumably as of ef0a81b2.
ECMA-48 has this weird concept that tab stops aren't necessarily the same across lines, and correspondingly, TBC with parameters 1, 2, 4 or 5 should only affect some of the lines. Plus, IMO its wording "character tabulation stop" and "line tabulation stop" is terrible; or maybe I don't understand exactly the concept.
DEC STD 070, EK-VT520-RM, xterm and ctlseqs don't have this concept. Tab stops are global (shared across all lines). Accordingly, TBC only accepts parameters 0 or 3; parameter values 1, 2, 4 or 5 are ignored.
vttest
emits TBC 1 and TBC 2 while the cursor is in row 1, and expects row 1's tab stops not to be cleared. That is, it explicitly tests that per-line tab stops are not supported.
We don't support per-line tab stops either, so it's probably wiser to follow xterm and make all of TBC 1, 2, 4, 5 a no-op, rather than some of them operating on the global tab stop columns.