Introduce interpreter factories

Introduce interpreter factories

If every UI instance has its own set of interpreters, then the current
scheme of creating the interpreters at GDB initialization time no
longer works.  We need to create them whenever a new UI instance is
created.

The scheme implemented here has each interpreter register a factory
callback that when called creates a new instance of a specific
interpreter type.  Then, when some code in gdb looks up an interpreter
(always by name), if there's none yet, the factory method is called to
construct one.

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

	* cli/cli-interp.c (cli_uiout): Delete, moved into ...
	(struct cli_interp): ... this new structure.
	(cli_on_normal_stop, cli_on_signal_received)
	(cli_on_end_stepping_range, cli_on_signal_exited, cli_on_exited)
	(cli_on_no_history): Use interp_ui_out.
	(cli_interpreter_init): If top level, set the cli_interp global.
	(cli_interpreter_init): Return the interp's data instead of NULL.
	(cli_interpreter_resume, cli_interpreter_exec, cli_ui_out): Adjust
	to cli_uiout being in the interpreter's data.
	(cli_interp_procs): New, factored out from _initialize_cli_interp.
	(cli_interp_factory): New function.
	(_initialize_cli_interp): Call interp_factory_register.
	* interps.c (get_interp_info): New, factored out from ...
	(get_current_interp_info): ... this.
	(interp_new): Add parameter 'data'.  Store it.
	(struct interp_factory): New function.
	(interp_factory_p): New typedef.  Define a VEC_P.
	(interpreter_factories): New global.
	(interp_factory_register): New function.
	(interp_add): Add 'ui' parameter.  Use get_interp_info and
	interp_lookup_existing.
	(interp_lookup): Rename to ...
	(interp_lookup_existing): ... this.  Add 'ui' parameter.  Don't
	check for NULL or empty name here.
	(interp_lookup): Add 'ui' parameter and reimplement.
	(interp_set_temp, interpreter_exec_cmd): Adjust.
	(interpreter_completer): Complete on registered interpreter
	factories instead of interpreters.
	* interps.h (interp_factory_func): New typedef.
	(interp_factory_register): Declare.
	(interp_new, interp_add): Adjust.
	(interp_lookup): Declare.
	* main.c (captured_main): Adjust.
	* mi/mi-interp.c (mi_cmd_interpreter_exec): Adjust.
	(mi_interp_procs): New, factored out from
	_initialize_mi_interp.
	(mi_interp_factory): New function.
	* python/python.c (execute_gdb_command): Adjust.
	* tui/tui-interp.c (tui_init): If top level, set the tui_interp
	global.
	(tui_interp_procs): New.
	(tui_interp_factory): New function.
	(_initialize_tui_interp): Call interp_factory_register.