Fix a crash bug reported by Jon Montroll.

ConnectionPool::peerConnect called Peer::connect while holding the
ConnectionPool::mPeerLock. But Peer::connect could call Peer::detach which
calls ConnectionPool::peerClosed which tries to acquire the
ConnectionPool::mPeerLock mutex. Said mutex was not recursive. Belt and
suspenders fix -- make the mutex recursive and make
ConnectionPool::peerConnection call Peer::connect without holding the
ConnectionPool::mPeerLock mutex. (This was intended to be a fast, internal
mutex and calls to external 'heavy' functions should not be made while
holding it.)

src/cpp/ripple/ConnectionPool.h

@@ -16,8 +16,8 @@
 class ConnectionPool
 {
 private:
-    boost::mutex	mPeerLock;
-    uint64			mLastPeer;
+    boost::recursive_mutex	mPeerLock;
+    uint64					mLastPeer;
 
 	typedef std::pair<RippleAddress, Peer::pointer>		naPeer;
 	typedef std::pair<ipPort, Peer::pointer>			pipPeer;