internal/ethapi: reduce pendingTransactions to O(txs+accs) from O(txs*accs)

metrics: fix gofmt linter warnings

* ethdb: gratefullly handle quit channel

* ethdb: minor polish

* core/rawdb: use wrappered helper to assemble key

* core/rawdb: wrappered helper to assemble key

* core/rawdb: rewrite the wrapper, pass common.Hash

trie: don't report the root flushlist as an alloc

rpc: support returning nil pointer big.Ints (null)

* core: improve getBadBlocks to return full block rlp

* core, eth, ethapi: changes to getBadBlocks formatting

* ethapi: address review concerns

The error produced when using a Parity RPC was the following:

ERROR: transaction did not get mined: failed to get tx for txid 0xbdeb094b3278019383c8da148ff1cb5b5dbd61bf8731bc2310ac1b8ed0235226: json: cannot unmarshal non-string into Go struct field txExtraInfo.blockHash of type common.Hash

This change introduces 

    ethkey changepassphrase <keyfile>

to change the passphrase of a key file.

optimization code

core: concurrent background transaction sender ecrecover

* trie: reduce hasher allocations

name    old time/op    new time/op    delta
Hash-8    4.05µs ±12%    3.56µs ± 9%  -12.13%  (p=0.000 n=20+19)

name    old alloc/op   new alloc/op   delta
Hash-8    1.30kB ± 0%    0.66kB ± 0%  -49.15%  (p=0.000 n=20+20)

name    old allocs/op  new allocs/op  delta
Hash-8      11.0 ± 0%       8.0 ± 0%  -27.27%  (p=0.000 n=20+20)

* trie: bump initial buffer cap in hasher

* vendor: added vendor packages necessary for the swarm-network-rewrite merge into ethereum master

* vendor: removed multihash deps

params: fix golint warnings

Allow the --abi flag to be given - to indicate that it should read the
ABI information from standard input. It expects to read the solc output
with the --combined-json flag providing bin, abi, userdoc, devdoc, and
metadata, and works very similarly to the internal invocation of solc,
except it allows external invocation of solc.

This facilitates integration with more complex solc invocations, such
as invocations that require path remapping or --allow-paths tweaks.

Simple usage example:

    solc --combined-json bin,abi,userdoc,devdoc,metadata *.sol | abigen --abi -

* tracing: fix minor off-by-one error

* tracers: go generate

core: fix typo in comment code

cmd: cap cache size if exceeds reasonable range

rpc: set timeouts for http server, see #16859

* metrics: expvar support for ResettingTimer

* metrics: use integers for percentiles; remove Overall

* metrics: fix edge-case panic for index-out-of-range

* core, eth, trie: streaming GC for the trie cache

* trie: track memcache statistics

Use Read instead of Sum to avoid internal allocations and
copying the state.

name                      old time/op  new time/op  delta
CacheGeneration-8          764ms ± 1%   579ms ± 1%  -24.22%  (p=0.000 n=20+17)
SmallDatasetGeneration-8  75.2ms ±12%  60.6ms ±10%  -19.37%  (p=0.000 n=20+20)
HashimotoLight-8          1.58ms ±11%  1.55ms ± 8%     ~     (p=0.322 n=20+19)
HashimotoFullSmall-8      4.90µs ± 1%  4.88µs ± 1%   -0.31%  (p=0.013 n=19+18)