programmatic metadata validation by the SP

[Peter Schober]

After a couple of changes to a metadata instance (mostly adding mdui
elements) which verified OK with xmllint and xmlsectool the SP
(2.4.3) complains with the following error, during `shibd -t`:

  2012-02-17 10:25:52 ERROR OpenSAML.MetadataProvider.XML : metadata
  intance failed manual validation checking: DisplayName must have
  TextContent.

Now the message is obvious enough, but I can't seem to find the
offending entry (tuning OpenSAML.MetadataProvider.XML to DEBUG log
level did not reveal any more info). But grepping and sorting
DisplayName elements from shows not a single one without what I
consider text content (in its ordinary language meaning, so I should
probably check the exact meaning of TextContent somewhere/the XSD).

Maybe the error message could be changed to include a line number or
some other way of identifying the offending entry (e.g. xpath to the
element, entityId of the containing EntityDescriptor, ...).

@Scott, Chad: you'll see this error on the SP at wiki.shibboleth.net
as well, as you also consume the metadata in question. In case you
find out what's wrong, please let me know ;)

cheers,
-peter