Move msgmerge-v.comp.po to mm-viet.comp.po.

diff --git a/gettext-tools/tests/msgmerge-v.comp.po b/gettext-tools/tests/mm-viet.comp.po
similarity index 100%
rename from gettext-tools/tests/msgmerge-v.comp.po
rename to gettext-tools/tests/mm-viet.comp.po