Force more frequent flushing
Allow to iterate over multi values when already iterating over the main tree
More features
Merge branch 'voron' of github.com:ayende/raven.voron into voron

Conflicts:
	Voron/StorageEnvironment.cs
proper write completed/errored handling when splitting
Better random generator)
super-cautious code when handling writes in background task
Better error exception to avoid users confusion that could happen if  they still have some free space on the disk (but not enough for us)
Merge branch 'voron' of github.com:ayende/raven.voron into voron
Merge branch 'voron' of https://github.com/ayende/raven.voron into voron
Minor - don't allocate a new string builder
fixed issue with sizeOfUnflushedTransactionsInJournalFile calculation
Merge branch 'voron' of https://github.com/ayende/raven.voron into voron
Merge branch 'voron' of https://github.com/ayende/raven.voron into voron
syncing data from journals to data file during recovery
precaution - we want to update headers when data is synced to disk
Ensure that FlushWritesToDataFileAsync will be run as separate background task. Also for background task set LongRunning option.
removing synced journal files, fixing issues with lastSyncedJournal calculation
Changing the esent column type to allow put values greater than 255 bytes
journal applicator should now calculate the pages to write correctly - removed delete marked in PageTable