RavenDB-2268 Introducing prefixed keys
RavenDB-2268 - Making voron aware of the introduced prefixed slice concept (half voron's tests is failing now)
RavenDB-2268 Instead of writing a new prefix during its creation, just mark that's a new prefix and write it when a node is created - it simplifies the way we can detect if the page has space for the node. Taking into account prefixes during page defragmentation.
RavenDB-2268 More fixes to get prefix compression working (~60 tests are failing at the moment)
RavenDB-2268 More fixes to get prefixed keys working (20 failing tests at this point)
RavenDB-2268 Do not increase the AvailablePrefixId value in the page header immediately because in case of a page splitting it can happen that there is no space and additional splits are needed (previous implementation broke the parent page when AddSeparatorToParentPage was called)
RavenDB-2268 Clear prefix offsets in a temp page header
RavenDB-2268 Fixing comparison sign
RavenDB-2268 Clear prefix info for a new allocated page
RavenDB-2268 Multi tree fix in ExpandMultiTreeNestedPageSize method - need to create prefixes when copy to a new page
RavenDB-2268 Tree rabalancer fixes - in order to merge pages use a temp page to properly control the size of added prefixed keys.
RavenDB-2268 New nested page must have empty prefix info
RavenDB-2268 Fixing new prefixed key creation in the tree rebalancer - preventing from doing very long prefix (when trying to add a key that already exists in a page - just rebalancing case when left implicit node is changed) [all voron's tests are green]
RavenDB-2268 Removing a lot of TODOs
RavenDB-2268 Introducing min length of a prefix - 20% of the key size
RavenDB-2268 Better prefix selection
RavenDB-2268 Rounding up the size of a stored prefix to an even number of bytes in order to ensure 2-byte alignment
Merge branch 'master' of git://github.com/ayende/ravendb into RavenDB-2268

Conflicts:
	Raven.Voron/Voron/Trees/Page.cs
	Raven.Voron/Voron/Trees/PageIterator.cs
	Raven.Voron/Voron/Trees/PageSplitter.cs
	Raven.Voron/Voron/Trees/Tree.MultiTree.cs
	Raven.Voron/Voron/Trees/Tree.cs
	Raven.Voron/Voron/Trees/TreeIterator.cs
Merge branch 'master' of git://github.com/ayende/ravendb into RavenDB-2268-common-slice-interface
RavenDB-2268 IMemorySlice interface introduction