Memory leak in error path and unnecessary assignment, from clang.
Remove the monitor-content option and associated bits and bobs. It's
never worked very well. If there is a big demand for it to return, will
consider better ways to do it.
Do not show the -fg, -bg and -attr options. If asked for one explicitly,
show the equivalent -style option instead.
Extend the -q flag to set-option to suppress errors about unknown
options - this will allow options to be removed more easily.
Remove the "info" message mechanism, this was only used for about five
mostly useless and annoying messages. Change those commands to silence
on success like all the others. Still accept the -q command line flag
and "quiet" server option for now.