execQueue used an atomic counter to track whether the queue had been
closed, but the checking the counter didn't happen because the queue was
blocked on its channel.

Fix it by using a condition variable instead of sync/atomic. I tried an
implementation based on channels first, but it was hard to make it
reliable.

quit now waits for the queue loop to exit.

Previously, resolve errors were being swallowed and the returned error
was a generic "not a content hash" which isn't helpful.

This updates the Resolve function to fail fast rather than only
returning an error at the end, and also adds test coverage.

CentOS has been added as a multi-machine option to the Vagrant script.
Ubuntu is still the default option. For starting the CentOS machine, use:

   vagrant up centos

mobile: add toString & rlp/json encoding for protocol types

cmd, node: support different bootnodes, fix default light port

core: fix processing regression during receipt import

common/bitutil: added data compression algorithm

travis: adapt build script to new travis VM settings

common/bitutil, consensus/ethash: reusable bitutil package

cmd, core, params: add --rinkeby flag for fast connectivity

* core: Fix for consensus test gasLimit > 2^63-1 https://github.com/ethereum/tests/blob/develop/BlockchainTests/bcInvalidHeaderTest.json#L238

* core: fix testcase for uncle gasUsage > gasLimit : https://github.com/ethereum/tests/blob/develop/BlockchainTests/EIP150/bcUncleHeaderValiditiy.json#L986

* math/big: rename TTM63m1 -> MaxBig63, + go fmt

* core: documentation

Migrate remaining flags/command to new style

cmd/faucet, cmd/puppeth: support multi-tiered faucet

build: wnode added to the build configuration

cmd/geth, cmd/utils: init/removedb on light/full dbs simultaneously

consensus/clique: fix overflow on recent signer check around genesis