Add additional comments to note incomplete validation of syntaxes

servers/slapd/schema/nis.schema

 # $OpenLDAP$
-# Definitions from RFC2307
+# Definitions from RFC2307 (Experimental)
+#	An Approach for Using LDAP as a Network Information Service
 
 # Note: The definitions in RFC2307 are given in syntaxes closely related
 # to those in RFC2252, however, some liberties are taken that are not
@@ -10,6 +11,9 @@
 # i.e. nisSchema in RFC2307 is 1.3.6.1.1.1
 #
 # Syntaxes are under 1.3.6.1.1.1.0 (two new syntaxes are defined)
+#	validaters for these syntaxes are incomplete, they only
+#	implement printable string validation (which is good as the
+#	common use of these syntaxes violates the specification).
 # Attribute types are under 1.3.6.1.1.1.1
 # Object classes are under 1.3.6.1.1.1.2