patch 8.0.1773: dialog messages are not translated

Problem:    Dialog messages are not translated.
Solution:   Add N_() and _() where needed. (Sergey Alyoshin)
diff --git a/src/po/Makefile b/src/po/Makefile
index fc78c43..386cb64 100644
--- a/src/po/Makefile
+++ b/src/po/Makefile
@@ -281,10 +281,10 @@
 checkclean:
 	rm -f *.ck
 
-$(PACKAGE).pot: ../*.c ../if_perl.xs ../GvimExt/gvimext.cpp ../globals.h ../if_py_both.h
+$(PACKAGE).pot: ../*.c ../if_perl.xs ../GvimExt/gvimext.cpp ../globals.h ../if_py_both.h ../vim.h
 	cd ..; $(XGETTEXT) --default-domain=$(PACKAGE) \
 		--add-comments --keyword=_ --keyword=N_ --keyword=NGETTEXT:1,2 \
-		*.c if_perl.xs GvimExt/gvimext.cpp globals.h if_py_both.h
+		*.c if_perl.xs GvimExt/gvimext.cpp globals.h if_py_both.h vim.h
 	mv -f ../$(PACKAGE).po $(PACKAGE).pot
 
 update-po: $(LANGUAGES)