ethdb: set open file limit to 128 for all leveldbs

eth: added a cancel method for the downloader

Added a cancel method to the downloader which gracefully shuts down any
active syncing process (hash fetching or block downloading) and resets
the queue and remove any pending blocks.

Issue with the downloader which would stall because of an active ongoing
process when an invalid block was found.

miner, flags: Configurable gas price & log flag change

* --gasprice "<num>" flag
* admin.miner.setGasPrice( <num> )

eth/downloader: prioritize block fetch based on chain position, cap memo...

p2p: more last-minute fixes

This should improve ethereum block propagation times since
we're not not broadcasting blocks to 100% of peers.

With the introduction of static/trusted nodes, the peer count
can go above MaxPeers. Update the capacity check to handle this.
While here, decouple the trusted nodes check from the handshake
by passing a function instead.

p2p: throttled handshakes

Otto.ToValue concurrency error fixed

jsre, cmd/geth: updated web3.js and altered settimeout

Test updates

solidity compiler and contract metadocs integration

xeth, core, event/filter, rpc: new block and transaction filters

Update ethash deps (more build fixes, tests)