readme: with 1.8 we need different default config
Test fixups because fallback css now always uses chunked encoding in 1.8.31.3
Version 1.8.31.2 -> 1.8.31.3
Clarify test name and test comment.
Merge pull request #714 from pagespeed/jmaessen-prepare-release-1.8.31.3-beta

Jmaessen prepare release 1.8.31.3 beta
Merge remote-tracking branch 'origin/release-1.8.31.3-beta'

Pulling in upstream merge to local master.