Refactor base_uint<>:
* Factor out common code, eliminate redundancies
* Change base_uint::ToString -> to_string(base_uint const&)
* Remove base_uint::GetHex
* Improve STAmount::getText, eliminate unnecessary copying
Use last closed ledger for old pathfinding
Rework handling of modified ledger nodes:
* Track dirty nodes in a set
* Make flushDirty a member function
* Don't write deleted nodes
* Make sure new nodes are shareable
* Put new nodes in the treeNodeCache
Keep SHAMapNodes that fault in handling client requests.
Comment and slight refactoring of RippleCalc.cpp.

* Restrict code to 80 columns.
* Extract a few local variables to help column length.
* Get rid of boost::format.
* Get rid of BOOST_FOREACH.
Comment and slight refactoring of RippleCalc.cpp (part 2)
Comment and slight refactoring of RippleCalc.cpp (part 3)
Clean up RippleCalc.h

* Make almost everything private.
* Rename member variables.
* Restrict to 80 columns.
* Add ripple::unordered_set to UnorderedContainers.h (renamed).
* Replace boolst::unordered_set with ripple::unordered_set.