Rewrite of choose mode, both to simplify and tidy the code and to add

some modern features.

Now the common code is in mode-tree.c, which provides an API used by the
three modes now separated into window-{buffer,client,tree}.c. Buffer
mode shows buffers, client mode clients and tree mode a tree of
sessions, windows and panes.

Each mode has a common set of key bindings plus a few that are specific
to the mode. Other changes are:

- each mode has a preview pane: for buffers this is the buffer content
  (very useful), for others it is a preview of the pane;

- items may be sorted in different ways ('O' key);

- multiple items may be tagged and an operation applied to all of them
  (for example, to delete multiple buffers at once);

- in tree mode a command may be run on the selected item (session,
  window, pane) or on tagged items (key ':');

- displayed items may be filtered in tree mode by using a format (this
  is used to implement find-window) (key 'f');

- the custom format (-F) for the display is no longer available;

- shortcut keys change from 0-9, a-z, A-Z which was always a bit weird
  with keys used for other uses to 0-9, M-a to M-z.

Now that the code is simpler, other improvements will come later.

Primary key bindings for each mode are documented under the commands in
the man page (choose-buffer, choose-client, choose-tree).

Parts written by Thomas Adam.

format.c

@@ -19,11 +19,9 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 
-#include <ctype.h>
 #include <errno.h>
 #include <fnmatch.h>
 #include <libgen.h>
-#include <netdb.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
@@ -840,7 +838,7 @@ format_choose(char *s, char **left, char **right)
 }
 
 /* Is this true? */
-static int
+int
 format_true(const char *s)
 {
 	if (s != NULL && *s != '\0' && (s[0] != '0' || s[1] != '\0'))