the order of the SchemaValidation filter

[Tom Scavo]

I cleaned up the notes re filter order throughout the MetadataProvider
documentation. In particular, I added a complementary note to the
SignatureValidation filter. I don't believe that needs to be reviewed
(but who knows given other stuff I've done lately :)

I have one remaining question regarding the SchemaValidation filter.
Does it matter where this filter appears in the overall list of
filters?

Thanks,

Tom