Change HBase StoreKey format

HBASE-859 cleaned up keys removing the need of HRegionInfo being in the context comparing keys. This issue is about changing the format. Work done in HBASE-859 means changes have been localized to HStoreKey, in particular to comparators and parse routines. We should do this now since 0.20.0 will require rewriting all data.

Things to consider:

<row> <columnfamily> <columnqualifier> <timestamp> <keytype>

Or leave off columnfamily altogether and just write it once into the hfile metadata (All key compares are done in the Store context so columnfamily can be safely left out of the equation; its only when the key rises above Store that the columnfamily needs appending).

keytype is probably a byte. Types are delete cell, delete row, delete family, delete column? What else? Where should we put it? At the end? How should type sort? Or should it not be part of sort so its just the order at which we encounter the key?

How are we going to support keys that go in out of chronological order?