Per-peer block download tracking and stalled download detection.

Keep track of which block is being requested (and to be requested) from
each peer, and limit the number of blocks in-flight per peer. In addition,
detect stalled downloads, and disconnect if they persist for too long.

This means blocks are never requested twice, and should eliminate duplicate
downloads during synchronization.
Display progress of rescan.
Add progress to initial display of latest block downloaded.
move wallet info stuff to "getwalletinfo" rpc (left original wallet
stuff in getinfo call for backwards compatibility)

add wallet transaction count to getwalletinfo rpc call
Remove unused includes of boost lexical_cast

We don't use lexical_cast anywhere, no need to include it.
Merge pull request #3514

f59d8f0 Per-peer block download tracking and stalled download detection. (Pieter Wuille)
doc/build-unix.md  use github flavored md for table
Transifex pull pre-0.9.0rc3/final
Merge pull request #3835

064a690 Transifex pull pre-0.9.0rc3/final (Wladimir J. van der Laan)
Merge pull request #3829

a75cacd doc/build-unix.md  use github flavored md for table (Torstein Husebø)
Merge pull request #3815

5283410 Remove unused includes of boost lexical_cast (Wladimir J. van der Laan)
qt: Remove control characters from ko_KR translation

Last Transifex pull (064a690) introduced a few control characters
into the Korean translation, which sometimes causes the build to fail.

Manually remove these characters for now to get the build working --
they should still be removed at Transifex too.
Merge pull request #3717 from djpnewton/wallet-txcount

add getwalletinfo RPC call with wallet transaction count
Make mining fee policy match relay fee policy.

This resolves a case in which a mismatch could be used to bloat up the
mempool by sending transactions that pay enough fee to relay, but not
to be mined, with the default policies.
qt: Make it possible again to specify -testnet in config file

Changes for the datadir chooser have made it impossible to specify
the network (testnet/regtest) in the configuration file for the GUI.

Reorganize the initialization sequence to make this possible again.

- Moves the "datadir" QSetting so that is no longer dependent on the
  network-specific application name (doing otherwise would create a
  chicken-and-egg problem).

- Re-initialize translations after choosing network. There may be a
  different language configured in network-specific settings
  (slim chance, but handle it for sanity).

Fixes point 1 of #3840.
Merge pull request #3696

c4656e0 Add progress to initial display of latest block downloaded. (R E Broadley)
75b8953 Display progress of rescan. (R E Broadley)
Merge branch 'match_relay_fee' of git://github.com/mikehearn/bitcoin
Merge pull request #3844

c52c4e5 qt: Make it possible again to specify -testnet in config file (Wladimir J. van der Laan)