JSA::WrapDR: filter argument for pre-capture clean

This allows a filename filtering function to be specified
for the clean_directory_pre_capture subroutine.
JSA::Convert: removed unused variable
JSA::Headers::Starlink:  add instream option

Added an "instream" option to the update_fits_headers
subroutine for use with streams other than "JCMT".
JSA::Convert: make ndf2fits public

This subroutine is required in UKIRT::Archive because
convert_to_fits is JSA-specific.
JSA::WrapDR: add use FindBin line
JSA::Headers: only call to_BACKEND if available