Fix wmllint confusing fake map border for fog

According to this: https://wiki.wesnoth.org/TerrainCodeTableWML
^_fme is Fake Map Border
_f is Fog

data/tools/wmllint

@@ -2882,7 +2882,7 @@ def translator(filename, mapxforms, textxform):
                     else:
                         fields = [x for x in line]
                     outmap.append(fields)
-                    if not maskwarn and maptype == 'map' and ("_f" in line or "_s" in line):
+                    if not maskwarn and maptype == 'map' and re.search('_s|_f(?!me)', line):
                         print('"%s", line %d: warning, fog or shroud in map file' \
                               % (filename, lineno+1))
                         maskwarn = True