[1866] added an empty .gitignore to keep the effectively-empty directory.

src/lib/dns/gen-rdatacode.py.in

@@ -181,7 +181,9 @@ def import_definitions(classcode2txt, typecode2txt, typeandclass):
             # also apply to files.
             filelist = os.listdir(classdir)
             filelist.sort()
-            if len(filelist) == 0: # if there's no known types treat it as meta
+            if len(filelist) == 0:
+                # if there's no known types treat it as meta.  Note that
+                # listdir() (seemingly) ignores .gitignore.
                 meta_classes[class_txt] = class_code
                 continue
             for file in filelist:

src/lib/dns/rdata/none_254/.gitignore

@@ -0,0 +1 @@
+# This file is here only for making the directory effectively empty.