Make settxfee clear that units are btc/kb.

Rebased-from: fffab7e45061aba3a5f345e0fc22a8584bcb012d 0.8.x
Fix minor unit test memory leaks

Rebased-from: 5d8c41f7b5eb1a103290f8c935127addeb781f73 0.8.x
Bitcoin-Qt: BitcoinGUI::message() updates/fixes

- ensure message boxes are shown in center of our main window, not
  centered on the users desktop
- always prefer user supplied titles for message boxes over the functions
  defaults (fixes a bug, where transaction info messages did not contain
  information, if it was incoming or outgoing)

Rebased-from: ca3c4d8d61d67f29c5db2b526cbfb5a4e7d9b727 0.8.x
misc small spelling/indentation fixes

Rebased-from: efde29e7f6b917bb4807157536dca400512ca99d 0.8.x
fix #3049 by changing comment for CNetAddr::IsRFC4193()

Rebased-from: 71888bf121a5abbfb89a693b9f2cb99935d3cfad 0.8.x
Bitcoin-Qt: prevent stuck/unusable debug window on exit

- when closing the client with an open debug window, that window could
  become stuck/unsuable (it was still shown wherea the main window was
  hidden already)
- fix this by hiding the debug window, when quitting the the client

Rebased-from: 3f8241c65539ceae7dc858f6f85acf3c2c58253b 0.8.x
Spelling fix in comment