Previously we only allow downloading of old blocks if the peer
difficulty was greater than our syncing difficulty. This change allows
downloading of blocks from peers where the difficulty is greater then
the last downloaded old block.
* Store recently rejected transactions.
* Don't cache AlreadyImported rejections.
* Make the size of transaction verification queue dependent on pool size.
* Add a test for recently rejected.
* Fix logging for recently rejected.
* Make rejection cache smaller.
* obsolete test removed
* obsolete test removed
* Construct cache with_capacity.
* Unordered iterator.
* Use unordered and limited set if full not required.
* Split timeout work into smaller timers.
* Avoid collecting all pending transactions when mining
* Remove println.
* Use priority ordering in eth-filter.
* Fix ethcore-miner tests and tx propagation.
* Review grumbles addressed.
* Add test for unordered not populating the cache.
* Fix ethcore tests.
* Fix light tests.
* Fix ethcore-sync tests.
* Fix RPC tests.
* Update `add_license` script
* run script
* add `remove duplicate lines script` and run it
* Revert changes `English spaces`
* strip whitespaces
* Revert `GPL` in files with `apache/mit license`
* don't append `gpl license` in files with other lic
* Don't append `gpl header` in files with other lic.
* re-ran script
* include c and cpp files too
* remove duplicate header
* rebase nit
