[search] Use 'AND' instead of 'OR' on search terms

The current search system uses the OR operator to concatenate search
terms. While results which are matched multiple times sort before
other matches, it is almost guaranteed that adding an additional term
to the search increments the number of results, which is rather
surprising.

https://bugzilla.gnome.org/show_bug.cgi?id=610955

js/ui/search.js

@@ -9,9 +9,10 @@ const RESULT_ICON_SIZE = 24;
 // implementations.
 const MatchType = {
     NONE: 0,
-    MULTIPLE: 1,
-    PREFIX: 2,
-    SUBSTRING: 3
+    SUBSTRING: 1,
+    MULTIPLE_SUBSTRING: 2,
+    PREFIX: 3,
+    MULTIPLE_PREFIX: 4
 };
 
 function SearchResultDisplay(provider) {
@@ -107,7 +108,7 @@ SearchProvider.prototype = {
 
     /**
      * getInitialResultSet:
-     * @terms: Array of search terms, treated as logical OR
+     * @terms: Array of search terms, treated as logical AND
      *
      * Called when the user first begins a search (most likely
      * therefore a single term of length one or two), or when
@@ -119,7 +120,8 @@ SearchProvider.prototype = {
      * item.  Ordering of returned results is up to the discretion of the provider,
      * but you should follow these heruistics:
      *
-     *  * Put items which match multiple search terms before single matches
+     *  * Put items where the term matches multiple criteria (e.g. name and
+     *    description) before single matches
      *  * Put items which match on a prefix before non-prefix substring matches
      *
      * This function should be fast; do not perform unindexed full-text searches