Rewrite of tmux mouse support which was a mess. Instead of having

options for "mouse-this" and "mouse-that", mouse events may be bound as
keys and there is one option "mouse" that turns on mouse support
entirely (set -g mouse on).

See the new MOUSE SUPPORT section of the man page for description of the
key names and new flags (-t= to specify the pane or window under mouse
as a target, and send-keys -M to pass through a mouse event).

The default builtin bindings for the mouse are:

    bind -n   MouseDown1Pane select-pane -t=; send-keys -M
    bind -n MouseDown1Status select-window -t=
    bind -n   MouseDrag1Pane copy-mode -M
    bind -n MouseDrag1Border resize-pane -M

To get the effect of turning mode-mouse off, do:

    unbind -n MouseDrag1Pane
    unbind -temacs-copy MouseDrag1Pane

The old mouse options are now gone, set-option -q may be used to
suppress warnings if mixing configuration files.

options-table.c

@@ -36,9 +36,6 @@
 const char *options_table_mode_keys_list[] = {
 	"emacs", "vi", NULL
 };
-const char *options_table_mode_mouse_list[] = {
-	"off", "on", "copy-mode", NULL
-};
 const char *options_table_clock_mode_style_list[] = {
 	"12", "24", NULL
 };
@@ -255,17 +252,7 @@ const struct options_table_entry session_options_table[] = {
 	  .default_str = "bg=yellow,fg=black"
 	},
 
-	{ .name = "mouse-resize-pane",
-	  .type = OPTIONS_TABLE_FLAG,
-	  .default_num = 0
-	},
-
-	{ .name = "mouse-select-pane",
-	  .type = OPTIONS_TABLE_FLAG,
-	  .default_num = 0
-	},
-
-	{ .name = "mouse-select-window",
+	{ .name = "mouse",
 	  .type = OPTIONS_TABLE_FLAG,
 	  .default_num = 0
 	},
@@ -575,12 +562,6 @@ const struct options_table_entry window_options_table[] = {
 	  .default_num = MODEKEY_EMACS
 	},
 
-	{ .name = "mode-mouse",
-	  .type = OPTIONS_TABLE_CHOICE,
-	  .choices = options_table_mode_mouse_list,
-	  .default_num = 0
-	},
-
 	{ .name = "mode-style",
 	  .type = OPTIONS_TABLE_STYLE,
 	  .default_str = "bg=yellow,fg=black"