Use VEC for filename_language_table

Use VEC for filename_language_table

This patch changes filename_language_table to be a VEC.  This seemed
like a reasonable cleanup over the old code.

2016-06-23  Tom Tromey  <tom@tromey.com>

	* symfile.c (filename_language_table): Now a VEC.
	(fl_table_size, fl_table_next): Remove.
	(add_filename_language): Use VEC_safe_push.
	(set_ext_lang_command, info_ext_lang_command)
	(deduce_language_from_filename): Use VEC_iterate.
	(init_filename_language_table): Use VEC_empty.