remove checksum test from ontology-version

As the checksum is no longer calculated we remove the test.
fix ontology-version spec for hets-api.
fix ontology-spec for hets-api and comment

The Ontology-DSL-using spec needed to be commented
out for now, until we've developed a strategy for this.
add rake task to freshen the fixtures.
remove ontology fixtures.
fix the hets-instance factory

The old version could only be used with
the local instance version.
fix the sentence spec for new spec-helpers.
add new helpers for hets-handling

Also fix the parse_this helper to use IO-objects instead
of file-paths (and drop the pp.xml).
Include Errors into GetCaller for UriFetcher.