its: During merge, copy also the XML node's attributes.
Rationale: In XHTML, attributes like 'style' are used for rendering.
* gettext-tools/src/its.c (_its_copy_node_with_attributes): New function.
(its_merge_context_merge_node): Use it.
* gettext-tools/tests/msgfmt-xml-1: Update expected results.
* gettext-tools/tests/msgfmt-xml-2: Likewise.
