slurm file only evaluated when validated cache changes

[reschke]

This is because updateFile exits early when fetching the cache yields a 304 (not modified), or if the hash of the cache did not change.

This is problematic for at least two reasons:

• it might be necessary to update the SLURM file in an emergency, in which case changes should become visible quickly,
• it makes testing/debugging extra hard (and the fact little activity is logged wrt slrum processing does not help).