from  Benoît Perrot  <benoit@lrde.epita.fr>

	Improve command identifiers recognition.

	* src/shell/cmd.hh: Rename
	(cmd_type_type, cmd_type_, get_type) as
	(identifier_type, id_, get_identifier) for readability.
	* src/shell/shell.hh (eat_word): Rename as 
	(eat_command_id) and move its implementation into...
	* src/shell/shell.cc: This file. Recognize uncomplete command
	identifiers and warn on ambiguity. Factor `build_cmd'.