Bug 15946 Valid namespace for OAI marcxml schema (3.22/3.20)

Bug 15946 Valid namespace for OAI marcxml schema (3.22/3.20)

As the patch for master, this patch apply on 3.22 (and 3.20 probably).

This path fixes the value of xml schema variable and the link to Library
of Congress.  For Dublin Core format those values are defined in
UNIMARCslim2OAIDC.xsl and MARC21slim2OAIDC.xsl.  For MARCXML those
values are written into the code

To test it:
1) Setup OAI-PMH
2) Test the site inserting the BaseURL into http://validator.oaipmh.com
3) See the problem with ListMetadataFormats [link:
   http://validator.oaipmh.com/#ListMetadataFormats] 4) Insert the patch
5) See the problem is over

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
  Invalid before patch, valid after.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
(cherry picked from commit 631b93204579bb2d85fc29af2500370449b07439)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>