Do not quote SRU = search if index is used by Z39.50

Do not quote SRU = search if index is used by Z39.50

We configure z39.50 to use the eg.keyword, eg.title, and eg.author
indexes.  One client in particular does "=" searches when it probably
means "all."  To give that client all of the results that it expects,
we modify SuperCat to not quote the terms of an = search when one of
the previous indexes is being used.

Signed-off-by: Jason Stephenson <jason@sigio.com>
Signed-off-by: Jason Boyer <JBoyer@library.in.gov>