Fix completer problem for filename completion on the first try.

	Fix completer problem for filename completion on the first try.

	* gdb/completer.h (gdb_completion_word_break_characters): New function.
	* gdb/completer.c: Include gdb_assert.h.
	(complete_line_internal_reason): New enum.
	(complete_line_internal): Change last argument type to
	complete_line_internal_reason.
	Modify function to handle the different complete_line_internal_reason
	argument values.
	(complete_line): Adapt to change in complete_line_internal.
	(command_completer): Ditto.
	(gdb_completion_word_break_characters): Implement new function.
	* top.c (init_main): Set  rl_completion_word_break_hook to
	gdb_completion_word_break_characters.