Refactor directive_domain and set_domain methods.

Refactor directive_domain and set_domain methods.

* gettext-tools/src/read-catalog-abstract.h
(abstract_catalog_reader_class_ty::directive_domain): Add name_pos parameter.
(catalog_reader_seen_domain): Likewise.
* gettext-tools/src/read-catalog-abstract.c (call_directive_domain,
catalog_reader_seen_domain): Likewise.
* gettext-tools/src/read-catalog.h
(default_catalog_reader_class_ty::set_domain): Add name_pos parameter.
(default_directive_domain, default_set_domain): Likewise.
* gettext-tools/src/read-catalog.c (call_set_domain, default_directive_domain):
Likewise.
(default_set_domain): Add name_pos parameter. Use it instead of the global
variable gram_pos.
* gettext-tools/src/msgfmt.c (msgfmt_set_domain): Likewise.
* gettext-tools/src/xgettext.c (exclude_directive_domain): Likewise.
* gettext-tools/src/po-gram-gen.y: Update catalog_reader_seen_domain invocation.