Concurrent SHAMap code
Use shared lock for SHAMap itself and concurrent map for nodes
Add RippleAsset types

Conflicts:
	Builds/VisualStudio2012/RippleD.vcxproj.filters
Add directory and order book iterators
This should fix the crossed order book bug.
* Change OfferCreate::takeOffers to use new iterators
* Change NetworkOps::getBookPage to use new iterators