Delete crashed if a fullNode contained a valueNode directly. This bug is
very unlikely to occur with SecureTrie, but can happen with regular
tries. This commit also introduces a randomised test which triggers all
trie operations, which should prevent such bugs in the future.

Credit for finding this bug goes to Github user @rjl493456442.

Package crypto needs cgo, which is inconvenient for some build
configurations.

README: Changed http:// to https:// on some links

core, trie: replace state caches with trie journal

Changed http:// to https:// on some links in README.md

cmd/utils: don't check for stderr redirect on windows

The redirect check did not work on Go 1.6 and below because Stat
returned an error for stdout and stderr. In Go 1.7 Stat works on stdout
but doesn't return anything meaningful, causing cmd/geth test failures
because the message is printed to stderr only. Fix it by printing to
stdout only.

build: limit test concurrency

TravisCI and AppVeyor run the tests in very slow VMs.
Some of our tests can't cope with that. Running less tests
in parallel should make them somewhat less flakey.

accounts/abi: fix typo in the comment (dummy commit)

State caching

This change introduces a global, per-state cache that keeps account data
in the canon state. Thanks to @karalabe for lots of fixes.

core/state: short-circuit balance change if zero value

light: fix memory expansion bug (same as fix for core/state)

ethclient: bugfix retrieving logs

core/state, light: remove unused StateObject.initCode

core/state: Fix memory expansion bug by not copying clean objects

cmd, eth: drop the blockchain version from cli/eth configs

miner: set tx index logs

rpc: format filter ID according to spec for quantities

core/types, ethclient: fix broken subscriptions

ethereum, ethclient: add SyncProgress API endpoint

cmd/evm, cmd/geth, cmd/utils: move version handling to cmd/utils