[CRIU] Merged some code from criu-dev into master

[Pavel Emelyanov]

Hello,

I've pulled some features that seem to work in criu-dev into master branch.

Eugene, the code for shmem changes tracking conflicted with the lack of
lazy pages in master :) Would you please, check that I resolved it correctly.

Dima, Laurent, the PMEM patches depended on c220f6da (sigframe: prepare macro 
helpers for two sigframes) which in turn sat in the x32 set, so I ported one
too. Would you also please check that I didn't break things.

Thanks!

-- Pavel