Revision 670124

HBASE-613 Timestamp-anchored scanning fails to find all records
HBASE-681 NPE in Memcache

HAbstractScanner
- remove HAbstactScanner.iterator() - iterator is not a method on InternalScanner

HRegion
- make getScanner more efficient by iterating only once to find the stores we need to scan
- only pass columns relevant to a store to a HStoreScanner
- remove HScanner.iterator() - iterator is not a method on InternalScanner

Memcache, MemcacheScanner
- Fix NPE in Memcache
- never return HConstants.LATEST_TIMESTAMP as the timestamp value for a row. Instead use the largest timestamp from the cells being returned. This allows a scanner to determine a timestamp that can be used to fetch the same data again should new versions be inserted later.

StoreFileScanner
- getNextViableRow would find a row that matched the row key, but did not consider the requested timestamp. Now if the row it finds has a timestamp greater than the one desired it advances to determine if a row with a timestamp less than or equal to the requested one exists since timestamps are sorted descending.
- removed an unnecessary else

testScanMultipleVersions
- Test program that fails on current trunk but passes when this patch is applied.