Specify a retrospective soft fork implemented in zcashd v2.1.1-1 that limits the nTime field of a block relative to its median-time-past. Correct the definition of median-time-past for the first PoWMedianBlockSpan blocks in a chain.
Specify a retrospective soft fork implemented in zcashd v2.1.1-1 that limits the nTime field
of a block relative to its median-time-past.
Correct the definition of median-time-past for the first PoWMedianBlockSpan blocks in a chain.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips