Add a --output=<DIR> option to ar to allow the specifying of an output directory.

Add a --output=<DIR> option to ar to allow the specifying of an output directory.

	* ar.c (emum long option numbers): Declare.  Use to provide
	numerical values for long options.
	(long_options): Add --output option.
	(usage): Mention the --output option.
	(open_output_file): New function.  Create a filepath for an output
	file and open it.
	(extract_file): Use open_output_file().
	(open_output_file):
	* testsuite/binutils-all/ar.exp: Add a test of the new feature.
	* doc/binutils.texi: Document the new feature.
	* NEWS: Mention the new feature.