(bug #4020) XSLT unimarc display

(bug #4020) XSLT unimarc display

When using XSLT Display, and UNIMARC,
since marcFlavour is not used in encoding data, when data is true utf8, as_xml
fails on some subfields.

Moreover, because transformMARCXMLForXSLT edits some values in the marc record
and the PERL UTF8 is not handled by MARC::File::USMARC, it endsup in double
encoding the data.
Sending a patch to fix both issues.

This patch adds
    - two functions in  C4/Charset.pm
        NormalizeString (uses Unicode::Normalize)
        SetUTF8Flag (This function in my opinion belongs to MARC::Record, or at least MARC::File::USMARC)
    - edits C4::XSLT in order to cope with the correct marcflavour
    - edits C4::Search searchResults to use setUTF8Flag