Support multiple text-match elements within a filter query.

Amended function SqlFilterFragment() to append a sequence number to the text-match parameter.
This allows comp-filters with multiple text-match elements to be properly supported, and is required to correctly implement RFC4791.
See section 9.7 of:
 http://www.ietf.org/rfc/rfc4791.txt
(Note that whilst an individual prop-filter may only have one text-match, comp-filters may have multiple prop-filters).