8683: Cover custom types on DTD and RNG files

Now, xmllint passes '--dtdvalid' and '--relaxng'

data/grampsxml.dtd

@@ -122,6 +122,7 @@ GENDER has values of M, F, or U.
 
 <!ELEMENT name    (first?, call?, surname*, suffix?, title?, nick?, familynick?, group?,
                   (daterange|datespan|dateval|datestr)?, noteref*, citationref*)>
+<!-- (Unknown|Also Know As|Birth Name|Married Name|Other Name) -->
 <!ATTLIST name    
         alt       (0|1) #IMPLIED
         type      CDATA #IMPLIED
@@ -138,6 +139,8 @@ GENDER has values of M, F, or U.
 <!ELEMENT familynick (#PCDATA)>
 <!ELEMENT group      (#PCDATA)>
 <!ELEMENT surname    (#PCDATA)>
+<!-- (Unknown|Inherited|Given|Taken|Patronymic|Matronymic|Feudal|
+Pseudonym|Patrilineal|Matrilineal|Occupation|Location) -->
 <!ATTLIST surname
         prefix      CDATA #IMPLIED
         prim        (1|0) #IMPLIED
@@ -196,12 +199,13 @@ FAMILY
 <!ELEMENT mother EMPTY>
 <!ATTLIST mother hlink IDREF #REQUIRED>
 
+<!-- (None|Birth|Adopted|Stepchild|Sponsored|Foster|Other|Unknown) -->
 <!ELEMENT childref (citationref*,noteref*)>
 <!ATTLIST childref
         hlink IDREF #REQUIRED
         priv  (0|1) #IMPLIED
-        mrel  (None|Birth|Adopted|Stepchild|Sponsored|Foster|Other|Unknown) #IMPLIED
-        frel  (None|Birth|Adopted|Stepchild|Sponsored|Foster|Other|Unknown) #IMPLIED
+        mrel  CDATA #IMPLIED
+        frel  CDATA #IMPLIED
 >
 
 <!ELEMENT type (#PCDATA)>