scraper.py: Scrapes Refresh header.

Closes chfoo/wpull#51.
recorder.py: Truncates the WARC file to safe offset if record fails to write.

Closes chfoo/wpull#52.
extended.py: read_from_fd returns None if buffer is nearing full.

chfoo/wpull#53
http_test.py: Removes skip on test_big.
Merge branch 'issue/53-fire-hose-ingress' into develop
changelog: Adds point about buffer size work around.
changelog: Updates latest to 0.22.5.
Merge branch 'develop'
Bumps version to 0.22.5.