added StripNonXmlChars to C4::Charset

added StripNonXmlChars to C4::Charset

Added invocations of StripNonXmlChars to uses
of new_from_xml() that involve records
saved to Koha fields via MARC::Record->as_xml();
for batch jobs that work on MARC XML files
coming from external sources, StripNonXmlChars
should not necessarily be used, as it may
be better to reject a file or record if it
contains that kind of encoding error.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>