Silence QP warning due to inappropriate cmp op

In QueryParser, we're comparing two strings, but using the numeric !=
operator. Switching to the 'ne' operator silences a warning that came up
7,000 today in our logs so far...

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>