Add isChannel column and meta attribute.

This is to properly separate channels from regular jobs and also make
sure that we can always iterate on them, no matter whether the build has
failed. The reason why we were not able to do this until now was because
we were iterating on the build products, and whenever some constituent
of a channel job has failed, we didn't get a build output.

So whenever there is a meta.isHydraChannel, we can now properly
distinguish it from the other jobs.

I still don't have any clue, why "make -C src/sql update-dbix" without
*any* modifications tries to create additional schema definitions. But
I've checked the md5sums of the existing schema definitions and they
don't seem to match, so it seems that they already have been tampered
with.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

src/sql/hydra.sql

@@ -157,6 +157,7 @@ create table Builds (
     maxsilent     integer default 3600, -- meta.maxsilent
     timeout       integer default 36000, -- meta.timeout
 
+    isChannel     integer default 0, -- meta.isHydraChannel
     isCurrent     integer default 0,
 
     -- Copy of the nixExprInput/nixExprPath fields of the jobset that