Trying to do hooks generically is way too complicated and unreliable and

confusing, particularly trying to automatically figure out what target
hooks should be using. So simplify it:

- drop before hooks entirely, they don't seem to be very useful;

- commands with special requirements now fire their own after hook (for
  example, if they change session or window, or if they have -t and -s
  and need to choose which one the hook uses as current target);

- commands with no special requirements can have the CMD_AFTERHOOK flag
  added and they will use the -t state.

At the moment new-session, new-window, split-window fire their own hook,
and display-message uses the flag. The remaining commands still need to
be looked at.

cmd-if-shell.c

@@ -165,7 +165,6 @@ cmd_if_shell_callback(struct job *job)
 	}
 
 	cmdq1 = cmdq_new(cmdq->client);
-	cmdq1->flags |= cmdq->flags & CMD_Q_NOHOOKS;
 	cmdq1->emptyfn = cmd_if_shell_done;
 	cmdq1->data = cdata;