Memory-conserving changes to SHAMapTreeNode and visitLeavesInternal.
Pathfinding performance improvements:
* Use a single RippleLineCache, even for 'fast' requests
* Use a ledger copy to avoid stalling other code
Suppress a warning.
Move some ledger cleaner helper functions into the ledger master.
Add a 1 MB payload limit to incoming websocket requests
Avoid an extraneous test.