Change some tests to give more insights.
* gettext-tools/tests/format-c-3-prg.c (_): Remove macro.
(main): Test also a simple translation.
* gettext-tools/tests/format-c-4-prg.c: Likewise.
* gettext-tools/tests/format-c-5-prg.c: Likewise.
* gettext-tools/tests/format-c-3: Update.
* gettext-tools/tests/format-c-4: Likewise.
* gettext-tools/tests/format-c-5: Likewise.
