Fix WARC writing bug#23

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jeffcasavant wants to merge 3 commits intointernetarchive:masterfrom

jeffcasavant:master

Commits on Jun 10, 2016

Add len function to FilePart
Jeff Casavant
committed
Write buf rather than payload instance
Jeff Casavant
committed
Remove length function to test if this isn't required
Jeff Casavant
committed