When the WM_QUOTE mode flag is set and the 'remsg' is specified, the original
message will quoted (excluding message tails, using the proper word-wrapping).
If the quote file already exists before calling postmsg()/bbs.post_msg(), it
will be over-written. This allows JS script to initiate reply-posts with quoted
text without having to create their own quotes file. It also means there's no
need to call sbbs_t::quotemsg() before calling sbbs_t::postmsg().
sbbs_t::quotemsg() now takes an smb_t* arg (stop using the sbbs_t 'global'
smb) and now returns bool.