PostgreSQL and Perl have different sort orders, in particular when
comparing job names such as "aspell.x86_64-linux" and
"aspellDicts.cs.i686-freebsd". This confused the evaluation
comparison code, causing some jobs to appear as "removed".
So now we do all the sorting in Perl.
Fixes#105.
The URI parameter "compare=..." can denote either an arbitrary
evaluation ID, or the name of a jobset in the same project. In the
latter case, the comparison is made against the latest completed
evaluation of the specified jobset.