Make instream be per UI

gdb/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* cli/cli-script.c (execute_user_command, read_next_line)
	(read_next_line): Adjust to per-UI instream.
	* event-top.c (stdin_event_handler, command_handler)
	(handle_line_of_input, command_line_handler)
	(gdb_readline_no_editing_callback, async_sigterm_handler)
	(gdb_setup_readline): Likewise.
	* inflow.c: Include top.h.
	(gdb_has_a_terminal, child_terminal_init_with_pgrp)
	(gdb_save_tty_state, child_terminal_inferior)
	(child_terminal_ours_1, copy_terminal_info): Use the main UI.
	(initialize_stdin_serial): Adjust to per-UI instream.
	* main.c (captured_command_loop, captured_main): Adjust to per-UI
	instream.
	* mi/mi-interp.c (mi_execute_command_wrapper): Likewise.
	* python/python.c (python_interactive_command): Likewise.
	* terminal.h (struct ui): Forward declare.
	(initialize_stdin_serial): Add struct ui parameter.
	* top.c (instream): Delete.
	(do_restore_instream_cleanup, read_command_file, dont_repeat)
	(gdb_readline_no_editing, command_line_input)
	(input_from_terminal_p, gdb_init): Adjust to per-UI instream.
	* top.h (struct ui) <instream>: New field.
	(instream): Delete declaration.
	(quit): Adjust to per-UI instream.

gdb/testsuite/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* gdb.gdb/selftest.exp (do_steps_and_nexts): Add new regexp.

gdb/utils.c

@@ -1047,10 +1047,12 @@ print_sys_errmsg (const char *string, int errcode)
 void
 quit (void)
 {
+  struct ui *ui = current_ui;
+
   if (sync_quit_force_run)
     {
       sync_quit_force_run = 0;
-      quit_force (NULL, stdin == instream);
+      quit_force (NULL, stdin == ui->instream);
     }
 
 #ifdef __MSDOS__