add --enable-debug for configure

Rebased-From: f5f157b
Transifex pull pre-0.9.0rc3/final

Rebased-From: 064a6905
doc/build-unix.md  use github flavored md for table

Rebased-From: a75cacd
Update release notes for 0.9.0rc3

No new features/bugfixes to be mentioned, but some authors have
contributed minor changes so add them to the credits.
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.

Rebased-From: 0ffd87f
Display progress of rescan.

Rebased-From: 75b8953
Add progress to initial display of latest block downloaded.

Rebased-From: c4656e0
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.

Rebased-From: 037b4f1
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.

Rebased-From: c52c4e5
Update release notes for mining change

Mining code fee policy now matches relay fee policy (1eedbbb)
Update the list of threads to the current state.
Fix release notes transaction fees
Warn about downgrading to 0.8.x

Fixes #3782
release notes: command line option is spendzeroconfchange

nospendzeroconfchange is valid as well on the command line,
but confusion about the name of the option was causing people to do things like
nospendzeroconfchange=0/1.