LP#1673799: new acqedim index to speed up duplicate file check

LP#1673799: new acqedim index to speed up duplicate file check

This patch adds a new index on acq.edi_message to speed up
the check for duplicate EDI messages that edi_fetcher.pl runs,
replacing use of "ilike" with invocations of the evergreen.lowercase()
stored procedure.

To test
-------
[1] Arrange to create or simulate an EDI message that failed
    processing.
[2] Run edi_fetcher.pl to have it attempt to download the
    failed message in step #1; verify that the file is
    /not/ downloaded again and that no additonal acq.edi_message
    rows are created for it.
[3] (Extra credit) Try steps 1 and 2 in a database that has a
    very large number of rows in acq.edi_message.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>