Allow build to be bumped to the front of the queue via the web interface

Builds now have a "Bump up" action. This will cause the queue runner
to prioritise the steps of the build above all other steps.

src/sql/hydra.sql

@@ -156,9 +156,13 @@ create table Builds (
     nixExprInput  text,
     nixExprPath   text,
 
-    -- Information about scheduled builds.
+    -- Priority within a jobset, set via meta.schedulingPriority.
     priority      integer not null default 0,
 
+    -- Priority among all builds, used by the admin to bump builds to
+    -- the front of the queue via the web interface.
+    globalPriority integer not null default 0,
+
     -- FIXME: remove (obsolete with the new queue runner)
     busy          integer not null default 0, -- true means someone is building this job now
     locker        text, -- !!! hostname/pid of the process building this job?
@@ -218,6 +222,10 @@ create function notifyBuildCancelled() returns trigger as 'begin notify builds_c
 create trigger BuildCancelled after update on Builds for each row
   when (old.finished = 0 and new.finished = 1 and new.buildStatus = 4) execute procedure notifyBuildCancelled();
 
+create function notifyBuildBumped() returns trigger as 'begin notify builds_bumped; return null; end;' language plpgsql;
+create trigger BuildBumped after update on Builds for each row
+  when (old.globalPriority != new.globalPriority) execute procedure notifyBuildBumped();
+
 #endif