Add timeoffset to getinfo RPC call

Provides a method to get the difference between network adjusted time
and local time from the RPC interface.
Various performance tweaks to CCoinsView

* Pass txid's to CCoinsView functions by reference instead of by value
* Add a method to swap CCoins, and use it in some places to avoid a
  allocating copy + destruct.
* Optimize CCoinsViewCache::FetchCoins to do only a single search
  through the backing map.
Native versions for AllocateFileRange()
Drop padding in blk* when finalizing file
Fix getbalance discrepency

Two changes:

Use IsConfirmed() instead of IsFinal(), so 'getbalance "*" 0' uses the same
'is this output spendable' criteria as 'getbalance'. Fixes issue #172.

And a tiny refactor to CWallet::GetBalance() (redundant call to IsFinal -- IsConfirmed
calls IsFinal).
getbalance with no arguments and 'getbalance "*" 0' could return different different results,
Reimplement click-to-pay links. Add OSX support.

Switch to using Qt's QLocalServer/QLocalSocket to handle bitcoin
payment links (bitcoin:... URIs)

Reason for switch: the boost::interprocess mechanism seemed flaky,
and doesn't mesh as well with "The Qt Way"

qtipcserver.cpp/h is replaced by paymentserver.cpp/h

Click-to-pay now also works on OSX, with a custom Info.plist
that registers Bitcoin-Qt as a handler for bitcoin: URLs and
an event listener on the main QApplication that handles
QFileOpenEvents (Qt translates 'url clicked' AppleEvents into
QFileOpenEvents automagically).
Enable dumpprivkey in safe mode
Change progress bar from block-based to time-based

This is less confusing to most people, and doesn't rely on estimates
of the total number of blocks received from other nodes.
Transactions-based verification progress
Internal RNG for approximateBestSubset to prevent degenerate behavior.

This fixes test_bitcoin failures on openbsd reported by dhill on IRC.

  On some systems rand() is a simple LCG over 2^31 and so it produces
an even-odd sequence.  ApproximateBestSubset was only using the least
significant bit and so every run of the iterative solver would be the
same for some inputs, resulting in some pretty dumb decisions.

Using something other than the least significant bit would paper over
the issue but who knows what other way a system's rand() might get us
here.  Instead we use an internal RNG with a period of something like
2^60 which is well behaved.  This also makes it possible to make the
selection deterministic for the tests, if we wanted to implement that.
reformat OS X build instrcs, add 10.8 + Homebrew

* reformatted the entire document to look pretty in both standard text and
  Markdown
* incorporated [my OS X 10.8 build instructions with Homebrew as the package
  manager](http://bitcoin.stackexchange.com/questions/3672/trouble-compiling-bitcoind-on-osx-with-homebrew/5253#5253)
* incorporated @gavinandresen's MacPorts and release build instructions based on
  an earlier revision of this commit
* added makefile patch necessary for Homebrew compilation to `contrib`
small changes in init, main, checkpoints.h and bitcoin-qt.pro

- remove an unneeded MODAL flag, as MSG_ERROR sets MODAL
- re-order an if-clause in main to have bool checks before a function call
- fix some log messages that used wrong function names
- make a log message use a correct ellipsis
- remove some unneded spaces, brackets and line-breaks
- fix style for adding files in the Qt project
Shorten a startup message. It was getting truncated and looks ugly.
Merge pull request #2325 from mikehearn/shortenmsg

Shorten a startup message. It was getting truncated and looks ugly.
Fix qt unit test build on OSX
Merge pull request #1974 from kjj2/walletnotify

Add -walletnotify to call an external script on wallet transactions
Merge pull request #2160 from petertodd/add-adjustedtime-to-rpc-getinfo

Add adjustedtime to getinfo RPC call
Merge pull request #2026 from colindean/doc/reformat-and-update-osx-instructions

reformat OS X build instrcs, add 10.8 + Homebrew
Merge pull request #2308 from apoelstra/safemode-privkey

Enable dumpprivkey in safe mode
Merge pull request #2312 from gmaxwell/random_random

ApproximateBestSubset internal RNG to prevent degenerate behavior.