xgettext: Make --directory option work right with Ruby input files.

xgettext: Make --directory option work right with Ruby input files.

* gettext-tools/src/xgettext.c (extract_from_file_func): Add found_in_dir
argument.
(xgettext_find_file): Return also the directory that was used to find the file.
(extract_from_file): Pass the directory to the extractor.
* gettext-tools/src/x-ruby.h (extract_ruby): Add found_in_dir argument.
* gettext-tools/src/x-ruby.c (extract_ruby): Add found_in_dir argument. Pass the
logical_filename to rxgettext, and run rxgettext in the given directory.
* gettext-tools/tests/xgettext-16: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add it.