Allow watching specific branches or any other search query

Any valid search string is now a valid filter expression or a
watched project.  The only operator not supported here is the
is:watched operator, because that creates a recursive call that
would never succeed.

The change turned out far bigger than it should be due to the request
scope requirement for the query builder.  We had to rearrange a lot
of code to ensure we always have the request scope available in order
to construct a query builder and execute the filter expressions.

Bug: issue 492
Change-Id: I199d9b215e000c049279cd8e86e7a36386fee0fb
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-server/src/main/java/com/google/gerrit/server/patch/PublishComments.java

@@ -284,7 +284,6 @@ public class PublishComments implements Callable<VoidResult> {
       cm.setPatchSet(patchSet, patchSetInfoFactory.get(patchSetId));
       cm.setChangeMessage(message);
       cm.setPatchLineComments(drafts);
-      cm.setReviewDb(db);
       cm.send();
     } catch (EmailException e) {
       log.error("Cannot send comments by email for patch set " + patchSetId, e);