Distinguish between permanent evaluation errors and transient input errors

Fixes #112.

src/sql/hydra.sql

@@ -62,6 +62,7 @@ create table Jobsets (
     keepnr        integer not null default 3,
     checkInterval integer not null default 300, -- minimum time in seconds between polls (0 = disable polling)
     schedulingShares integer not null default 100,
+    fetchErrorMsg text,
     primary key   (project, name),
     foreign key   (project) references Projects(name) on delete cascade on update cascade
 #ifdef SQLITE

src/sql/upgrade-22.sql

@@ -0,0 +1 @@
+alter table Jobsets add column fetchErrorMsg text;