Merge pull request #2452 from Diapolo/Qt_fix_GUI

Bitcoin-Qt: fix GUI after initial multi-wallet patch
Merge pull request #2450 from Diapolo/Qt_fix_VMTab

Bitcoin-Qt: fix opening verify message tab via main menu
Fix signed/unsigned comparison warnings
Shutdown cleanup prep-work

Create a boost::thread_group object at the qt/bitcoind main-loop level
that will hold pointers to all the main-loop threads.

This will replace the vnThreadsRunning[] array.

For testing, ported the BitcoinMiner threads to use its
own boost::thread_group.
Rename util.h Sleep --> MilliSleep

Two reasons for this change:
1. Need to always use boost::thread's sleep, even on Windows, so the
sleeps can be interrupted (prior code used Windows' built-in Sleep).

2. I always forgot what units the old Sleep took.
Bitcoin-Qt: updates to addressbookpage

- use labelExplanation for sending and receiving tab and move the string
  from the ui-file to the source
- ensure that the table holding the label and address is resized so that
  the address column fits the address and the label column is stretched to
  fit the window size
- rename some stuff for much easier readbility in the code (I find it hard
  to get the meaning of stuff like labels or buttons)
LoopForever and ThreadTrace helpers
Port Thread* methods to boost::thread_group
Clean up shutdown process
Have Qt poll for shutdown requested, the QT way.
Update transaction statistics

As these were not updated when 'backporting' the 225430 checkpoint
into head.

Additionally, also report verification progress in debug.log, and
tweak the sigcheck-verification-speed-factor a bit.
Merge pull request #2453 from sipa/txstats

Update transaction statistics
Merge pull request #2357 from gavinandresen/shutdowncleanup

Thread / shutdown cleanup
Merge pull request #2449 from Diapolo/doc

move multiwallet-qt.txt from root to doc folder
Merge pull request #2423 from TheBlueMatt/limitedmapalreadyaskedfor

Limited mapAlreadyAskedFor
Fix leveldb make flags.
add missing limitedmap.h to bitcoin-qt.pro
Drop release times for CNode

It seems there were two mechanisms for assessing whether a CNode
was still in use: a refcount and a release timestamp. The latter
seems to have been there for a long time, as a safety mechanism.

However, this timer also keeps CNode objects alive for far longer
than necessary after disconnects, potentially opening up a DoS
window.

This commit removes the timestamp-based mechanism, and replaces
it with an assert(nRefCount >= 0), to verify that the refcounting
is indeed correctly working.
Merge pull request #2455 from Diapolo/pro-file

add missing limitedmap.h to bitcoin-qt.pro
Merge pull request #2454 from TheBlueMatt/master

Fix leveldb make flags in bitcoin-qt.pro