Put XPath offset validation behind a configuration knob.
Put XPath offset validation behind a configuration knob.

This step validates that generated XPath expressions match the source
document.  While this validation can catch some hard-to-debug issues,
it is also extremely expensive.  Disable it by default but let configuration
turn it back on.

trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline,trec-kba/streamcorpus-pipeline