configure: check for Xapian extended wildcard support

configure: check for Xapian extended wildcard support

Xapian 2.0 supports extended wildcard queries in the query parser. To
quote the NEWS file:

    WILDCARD_PATTERN_MULTI (which supports `*` wildcards anywhere in
    the term, not just at the end as previously),
    WILDCARD_PATTERN_SINGLE (which supports `?` wildcards matching a
    single character), and WILDCARD_PATTERN_GLOB which enables both of
    these.

This commit does not add any functionality, just detects if this
support is there in Xapian.