Show only one zero instead of many when getblocks request received with a hashStop of uint256(0)
doc: Add historical release notes for 0.9.2

Also includes 0.9.2.1
Merge pull request #4434

3f1ea91 doc: Add historical release notes for 0.9.2 (Michael Ford)
Merge pull request #3990

0dd5d3a Show only one zero instead of many when getblocks request received with a hashStop of uint256(0) (R E Broadley)
Make CBlockIndex a subclass of CBlockHeader
Unify CBlockHeader::hashPrevBlock and CDiskBlockIndex::hashPrev
Unify GetHash() and GetBlockHash()
Remove GetBlockHeader()
CBlockIndex* CDiskBlockIndex::CreateIndex() instead of manual mapping