This commit replaces the deep-copy based state revert mechanism with a
linear complexity journal. This commit also hides several internal
StateDB methods to limit the number of ways in which calling code can
use the journal incorrectly.

As usual consultation and bug fixes to the initial implementation were
provided by @karalabe, @obscuren and @Arachnid. Thank you!

internal/build: use less edgy command to get the branch name

core/state: track dirty state entries for each object

build: improve debian packaging

This commit tweaks the debian packaging tool:

* All build environment metadata can now be overriden on the command
  line. This allows testing the CI build behaviour locally.
* -unstable packages now actually contain the binaries (oops)
* packages use Go 1.7 to build
* archiving is skipped for PR builds

crypto/sha3: update from golang.org/x/crypto/sha3 a 80b25ed4

This pulls in the assembly implementation of keccakf1600 for amd64.

cmd, core, internal, light, tests: avoid hashing the code in the VM

trie: fix delete bug for values contained in fullNode

accounts: left pad keybytes-to-encrypt

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.

cmd/utils, node: make datadir reusable for bzzd

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