add .gitignore file (same as .cvsignore) in "po" dir.

po/.gitignore

@@ -1 +1,25 @@
+*.cat
 *.gmo
+*.mo
+*.msg
+*.pox
+Makefile
+Makefile.in
+Makefile.in.in
+Makevars.template
+POTFILES
+POTFILES.in
+POTFILES.in.missing
+Rules-quot
+boldquot.sed
+cat-id-tbl.c
+en@boldquot.header
+en@quot.header
+insert-header.sin
+mc.pot
+messages
+quot.sed
+remove-potcdate.sed
+remove-potcdate.sin
+stamp-cat-id
+stamp-po