tests/test-gendoc-it.t

lfs: gracefully handle aborts on the server when corrupt blobs are detected

The aborts weren't killing the server, but this seems cleaner.  I'm not sure if
it matters to handle the remaining IOError in the test like this, for
consistency.

The error code still feels wrong (especially if the client is trying to download
a corrupt blob) but I don't see anything better in the RFCs, and this is already
used elsewhere because the Batch API spec specifically mentioned this as a
"Validation Error".

#require docutils gettext

  $ $TESTDIR/check-gendoc it
  checking for parse errors