Quark 0.10.4.3

https://github.com/quark-project/quark/releases/tag/v0.10.4.3

Important notice

For Quark 0.9 users this is a required upgrade.

Changes in this release

* Adds checkpoints on contentious blocks
* Disconnect from older 0.9 peers
* Turn default for automatic mining to "off" in the QT wallet.
* Fix difficulty value displayed for rpc commands