schedule hardfork
new block timestamp limits

past: time of last block
future: +15 seconds
change block time from 60 to 64 seconds
new stake protocol
block version 7

use double sha256 instead of scrypt for block hash
using scrypt provides no advantage and is orders of magnitude slower
adapt stake miner to new protocol
adapt GetStakeWeight() to new protocol
adapt GetPoSKernelPS() to new protocol
remove mention of -staking from help
round displaying weight up to coin
update split/combine thresholds for new protocol
update pos target limit
sync translations
bump version
add checkpoint
update checkpoint
disable check for min proof after checkpoint

as it may cause network split
bump version
Update readme-qt.rst

Otherwise the compilation exits with the error because miniupnpc is required
but not installed.
add OpenSSL RAND_cleanup() on OpenSSL shutdown

- to securely erase the memory used by the PNRG
- also rework 2 comments in OpenSSL init