query.c: Added the + keyword modified

Using + adds the associated keyword to the result, ignoring all previous filters.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
query.c: Support the "in-" prefix to keywords

Searching for "in-name:foo" will scan the entire index table for entries like
"name:%foo%".

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
query.c: Deal with repeated entries

Index entries may be repeated if they are associated with several different
scores.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>