Disable auto compositions on the Linux console only

Disable auto compositions on the Linux console only

* lisp/term/linux.el (terminal-init-linux): Disable auto
compositions on "linux" consoles (bug#21363).

* src/composite.c (inhibit_auto_composition): New function to
implement this.
(composition_compute_stop_pos, composition_adjust_point)
(Ffind_composition_internal): Use it.
(syms_of_composite): Document it.

* src/lisp.h: Export tty_type_name.

* src/term.c (tty_type_name): Factored out.
(Ftty_type): Use it.