Tidy up and improve target (-t) argument parsing:

- move the code back into cmd.c and merge with the existing functions where
  possible;
- accept "-tttyp0" as well as "-t/dev/ttyp0" for clients;
- when looking up session names, try an exact match first, and if that fails
  look for it as an fnmatch pattern and then as the start of a name - if more
  that one session matches an error is given; so if there is one session called
  "mysession", -tmysession, -tmysess, -tmysess* are equivalent but if there
  is also "mysession2", the last two are errors;
- similarly for windows, if the argument is not a valid index or exact window
  name match, try it against the window names as an fnmatch pattern and a
  prefix.

Makefile

@@ -1,7 +1,7 @@
 # $OpenBSD$
 
 PROG=	tmux
-SRCS=	arg.c attributes.c buffer-poll.c buffer.c cfg.c client-fn.c \
+SRCS=	attributes.c buffer-poll.c buffer.c cfg.c client-fn.c \
 	client-msg.c client.c clock.c cmd-attach-session.c cmd-bind-key.c \
 	cmd-break-pane.c cmd-choose-session.c cmd-choose-window.c \
 	cmd-clear-history.c cmd-clock-mode.c cmd-command-prompt.c \