Some additional renames in timestamp cache and also a fix to not cache
timestamps earlier than the high water mark. This doesn't affect
correctness, just is slightly more efficient. No need to cache old
timestamps (e.g. from historical reads).
Merge pull request #59 from cockroachdb/spencerkimball/timestamp-cache-improvement

Some additional renames in timestamp cache and also a fix to not cache
Implement and unittest EndTransaction.

Added an implementation for EndTransaction which attempts to move a
transaction from PENDING to either COMMITTED or ABORTED depending on
the EndTransactionRequest.Commit argument. Various error conditions
may result, including the txn already being committed or aborted,
Epoch or timestamp regressions, or transaction retry on SSI txns
in the event that the commit timestamp is different from the transaction
timestamp.
Merge pull request #60 from cockroachdb/spencerkimball/end-transaction

Implement and unittest EndTransaction.
Added pprof tools and exported variables via the /debug URL prefix.
Also added a handler for listing all goroutine stack traces.

Added unittests for all of the above.