FYI: Upstream sync

[Roman Kennke]

Hello all,

I synced the Lilliput repo with latest upstream. Most notably, this 
dragged in the removal of BiasedLocking, which caused a number of merge 
conflicts and also required to re-instate some of the biased-locking 
code paths because we use them in Lilliput. In particular, the 
Klass::_prototype_header field is back and used to populate initial 
headers of all objects.

Thanks,
Roman