Re-implement log size limits

The old queue runner already had this. However, we now store "log
limit exceeded" as a separate status code in the database.

src/root/build.tt

@@ -59,6 +59,8 @@
                 <span class="error">Cached failure</span>
               [% ELSIF step.status == 9 %]
                 <span class="error">Unsupported system type</span>
+              [% ELSIF step.status == 10 %]
+                <span class="error">Log limit exceeded</span>
               [% ELSIF step.errormsg %]
                 <span class="error">Failed: [% HTML.escape(step.errormsg) %]</span>
               [% ELSE %]