- if a revisit is of a redirect (3xx response) and revisit has http headers, return
the http headers with empty payload -- don't bother loading the original record
builds on changes in #751
- cleanup redirect revisit tests from #751
* revisit loading fix for revisit records with http headers:
- if revisit record has http headers, always use those headers
- otherwise, continue to use http headers from payload record
- parse headers of http and payload records on initial lookup, to simplify loading
- tests: add test for loading revisit records with different urls, different headers but same payload
- fix for sul-dlss/was-pywb#64
* also bump version to 2.6.8