LT-15805: Crash on every S/R Lexicon

* increase the maximum commit log size in SharedXMLBackendProvider
* add ability to create surrogate from an XML byte array
* SharedXMLBackendProvider now throws more informative exceptions
* change SharedXMLBackendProvider so it will not throw an exception
when the master fills the commit log
* make commit log size configurable via the registry

Change-Id: I64721c27a9140c9adbee3a78914bddd05bcfd157