Preserve ST or BEL in query responses
xtermcontrol --get-bg and friends hang as of vte-0.54 rather than reporting the desired value.
We used to respond with ST or BEL terminator, whichever the query was terminated with (matching xterm's behavior). As of the parser rewrite the response always terminates with ST. Apparently this is not understood by xtermcontrol.
If a "?" is given rather than a name or RGB specification, xterm replies with a control sequence of the same form
I interpret this "of the same form" as we should preserve the terminator.
Christian, what do you think?