window or session (which can happen if it is killed during a command
sequence and something else has a reference), fall back to the best
effort. Fixes "tmux killw\; detach" for Rudis Muiznieks.
server at a time; it may be toggled or cleared with select-pane -m and
-M (the border is highlighted). A new target '~' or '{marked}' specifies
the marked pane to commands and it is the default target for the
swap-pane and join-pane -s flag (this makes them much simpler to use -
mark the source pane and then change to the target pane to run swapp or
joinp).
consistent but with much less duplication, but keeping the same internal
API. Also adds more readable aliases for some of the special tokens used
in targets (eg "{start}" instead of "^"). Some behaviours may have
changed, for example prefix matches now happen before fnmatch.
