Changing the method name and removing invalid check
Ensuring that even if an operation causes exception it will be written to the debug journal
Fixing debug journal issue that loading from a file trimmed a few first characters of debug journal - no need to initialize journal twice (in ctor an LoadMethod)
A few fixes with regards to optional prefixed keys usage
Voron fixes after prefixed keys concept introduction:

* GetNodeKey method has to copy the slice data and cannot relay on pointers because after a page defrag operation they can change and points to invalid positions
* fixing a condition in if statement of TreeRebalancer.GetActualKey method - prevent from creating empty prefixed keys
* added a missing prefix info clean up of a new nested page of a multi tree
Deleting unnecessary assigns of last search position of a parent page in TreeRebalancer
Merge branch 'master' of git://github.com/ayende/ravendb into RavenDB-2482

Conflicts:
	Raven.Voron/Voron/Impl/TransactionMergingWriter.cs