Commit 40cdcf11 broke the optimisation which kept nodes resolved
during Get in the trie. The decoder assigned cache generation 0
unconditionally, causing resolved nodes to get flushed on Commit.

This commit fixes it and adds two tests.

New checks whether the root node is present by loading it from the
database. Keep the node around instead of discarding it.

trie: fix regression that linked all downloaded nodes together

params: set reprice block number to 2463000

The trie sync code links subtries using pointers into node structs.
Since commit 40cdcf11 nodes are no longer copied when unpacking from
an interface value, causing all nodes to get linked up as the sync
progresses. Fix it by breaking the pointer chain with an explicit copy.

core, core/vm: added gas price variance table (EIP #150)

core: add global (soft) limits on the pending transactions

This implements 1b & 1c of EIP150 by adding a new GasTable which must be
returned from the RuleSet config method. This table is used to determine
the gas prices for the current epoch.

Please note that when the CreateBySuicide gas price is set it is assumed
that we're in the new epoch phase.

In addition this PR will serve as temporary basis while refactorisation
in being done in the EVM64 PR, which will substentially overhaul the gas
price code.

* trie: store nodes as pointers

This avoids memory copies when unwrapping node interface values.

name      old time/op  new time/op  delta
Get        388ns ± 8%   215ns ± 2%  -44.56%  (p=0.000 n=15+15)
GetDB      363ns ± 3%   202ns ± 2%  -44.21%  (p=0.000 n=15+15)
UpdateBE  1.57µs ± 2%  1.29µs ± 3%  -17.80%  (p=0.000 n=13+15)
UpdateLE  1.92µs ± 2%  1.61µs ± 2%  -16.25%  (p=0.000 n=14+14)
HashBE    2.16µs ± 6%  2.18µs ± 6%     ~     (p=0.436 n=15+15)
HashLE    7.43µs ± 3%  7.21µs ± 3%   -2.96%  (p=0.000 n=15+13)

* trie: close temporary databases in GetDB benchmark

* trie: don't keep []byte from DB load around

Nodes decoded from a DB load kept hashes and values as sub-slices of
the DB value. This can be a problem because loading from leveldb often
returns []byte with a cap that's larger than necessary, increasing
memory usage.

* trie: unload old cached nodes

* trie, core/state: use cache unloading for account trie

* trie: use explicit private flags (fixes Go 1.5 reflection issue).

* trie: fixup cachegen overflow at request of nick

* core/state: rename journal size constant

metrics, internal/debug: Add --pprofaddr flag, expose metrics via gexp

swarm: fix http API's last problems

swarm/storage: Allow EOF at the end of the reader in the chunker. Handle the case when Read returns less than length of target slice

swarm/storage: fixes for tree chunker in the context of a broken reader

core: fixed import reporter

* brokenLimitedReader gives error after half size
* TestRandomBrokenData tests chunker with broken reader
* add blocking quitC (instead of errC) and use errC only for errors
* don't close chunkC in tester Split,
* use quitC to quit chunk storage loop

core: print import stats more often

core: lower transaction pool max queue limit

If geth is busy importing 2048 heavy blocks it can take a while before
it prints anything. This change ensures that a message gets printed
every 8s.

core/types: renamed receiptRoot to receiptsRoot

tests: update test files from github.com/ethereum/tests @ 45bc1d21d3c1

core/state: implement reverts by journaling all changes

Two new tests are skipped because they're buggy. Making some newer
random state tests work required implementing the 'compressed return
value encoding'.

There is no need to use the reflection-based decoder to decode []byte.

The delete/remove naming has caused endless confusion in the past.

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!

eth: monitor malicious header retrieval requests

internal/ethapi: bugfix gas price and limit swapped in eth_resend

rpc: set CORS Max-Age to reduce preflight OPTIONS requests

internal/build: fix git tag env variable for AppVeyor