receipts may be null for very short time in some condition. For this case, we should not add the null value into cache. Because you will not get the right result if you keep requesting that receipt.

* swarm/network: fix data race in stream.(*Peer).handleOfferedHashesMsg()

handleOfferedHashesMsg() contained a data race:
- read => in a goroutine, call to c.batchDone()
- write => in the main thread, write to c.sessionAt

c.batchDone() contained a call to c.AddInterval(). Client was a value
receiver for AddInterval. So on c.AddInterval() call the whole client
struct got copied (read) while one of its field was modified in
handleOfferedHashesMsg() (write).

fixes ethersphere/go-ethereum#1086

* swarm/network: simplify some trivial statements

core, light: get rid of the dual mutexes, hard to reason with

* swarm/network: fix skipped tests related to suggestPeer

* swarm/network: rename depth to radius

* swarm/network: uncomment assertHealth and improve comments

* swarm/network: remove commented code

* swarm/network: kademlia suggestPeer algo correction

* swarm/network: kademlia suggest peer

 * simplify suggest Peer code
 * improve peer suggestion algo
 * add comments
 * kademlia testing improvements
   * assertHealth -> checkHealth (test helper)
   * testSuggestPeer -> checkSuggestPeer (test helper)
   * remove testSuggestPeerBug and TestKademliaCase

* swarm/network: kademlia suggestPeer cleanup, improved comments

* swarm/network: minor comment, discovery test default arg

* cmd/swarm/swarm-snapshot: add binary to create network snapshots

* cmd/swarm/swarm-snapshot: refactor and extend tests

* p2p/simulations: remove unused triggerChecks func and fix linter

* internal/cmdtest: raise the timeout for killing TestCmd

* cmd/swarm/swarm-snapshot: add more comments and other minor adjustments

* cmd/swarm/swarm-snapshot: remove redundant check in createSnapshot

* cmd/swarm/swarm-snapshot: change comment wording

* p2p/simulations: revert Simulation.Run from master

https://github.com/ethersphere/go-ethereum/pull/1077/files#r247078904

* cmd/swarm/swarm-snapshot: address pr comments

* swarm/network/simulations/discovery: removed snapshot write to file

* cmd/swarm/swarm-snapshot, swarm/network/simulations: removed redundant connection event check, fixed lint error

fixes: ethersphere/go-ethereum#1117

* Update copyright

2018 -> 2019

* Update copyright

2018 -> 2019

params: postpone Constantinople due to net SSTORE reentrancy

* swarm/pot: refactored pot.remove(), updated comments

* swarm/pot: comments updated

* swarm/network: eachBin now starts at kaddepth for nn

* swarm/network: fix Kademlia.EachBin

* swarm/network: fix kademlia.EachBin

* swarm/network: correct EachBin implementation according to requirements

* swarm/network: less addresses simplified tests

* swarm: calc kad depth outside loop in EachBin test

* swarm/network: removed printResults

* swarm/network: cleanup imports

* swarm/network: remove kademlia.EachBin; fix RequestSubscriptions and add unit test

* swarm/network/stream: address PR comments

* swarm/network/stream: package-wide subscriptionFunc

* swarm/network/stream: refactor to kad.EachConn

* core, eth: fix database version

* eth: polish error message

Co-authored-by: weimumu <934657014@qq.com>

* swarm/network: Rename minproxbinsize, add as member of simulation

* swarm/network: Deactivate WaitTillHealthy, unreliable pending suggestpeer

* swarm/network, swarm/pss: remove isproxbin bool from kad.Each* iterfunc

* swarm/network: restore comment and unskip snapshot sync tests

* swarm/storage: fix T.Fatal inside a goroutine

* swarm/network/simulation: fix T.Fatal inside a goroutine

* swarm/network/stream: fix T.Fatal inside a goroutine

* swarm/network/simulation: consistent failures in TestPeerEventsTimeout

* swarm/network/simulation: rename sendRunSignal to triggerSimulationRun

* swarm: completed 1st phase of swap accounting

* swarm, p2p/protocols: added stream pricing

* swarm/network/stream: gofmt simplify stream.go

* swarm: fixed review comments

* swarm: used snapshots for swap tests

* swarm: custom retrieve for swap (less cascaded requests at any one time)

* swarm: addressed PR comments

* swarm: log output formatting

* swarm: removed parallelism in swap tests

* swarm: swap tests simplification

* swarm: removed swap_test.go

* swarm/network/stream: added prefix space for comments

* swarm/network/stream: unit test for prices

* swarm/network/stream: don't hardcode price

* swarm/network/stream: fixed invalid price check

* Changed dumpConfig function to optionally save to file

* Added O_TRUNC flag to file open and cleaned up code

* swarm/network: fix code inspection problems

- typos
- redundant import alias

* p2p/simulations: fix code inspection problems

- typos
- unused function parameters
- redundant import alias
- code style issue: snake case

* swarm/network: fix unused method parameters inspections

* eth/tracer: extend create2

* eth/tracers: fix create2-flaw in prestate_tracer

* eth/tracers: fix test

* eth/tracers: update assets

core/types: update incorrect comment