Call, Prepare/Flush, and RunTransaction examples.

Example functions for a simple Put & Get using Call(), Prepare() &
Flush(), and then RunTransaction().

Each example is self-contained, and includes the server
setup/teardown.  This makes the code closer to what would be used in
an actual client program.

Named all examples so that they will appear in the correct section
of the documentation.

The Prepare() & Flush() is a bit long because we have to create the values
we are later scanning for.

All the examples have been updated to match the coding style and
fix other issues.  Prepare/Flush example now runs multiple scans for
sub-ranges of the keys in parallel.
Fix double space.
Don't specify isolation level in transaction.
Merge pull request #178 from jamesgraves/client_examples

Example code for basic Call and Prepare/Flush.
fix a (rare and testing-only) data race
Remove all instances in test code which use a zero timestamp.

This is in preparation of using a zero timestamp to mean an inline
MVCC value so we can avoid ever using the engine directly and instead
write all data through the MVCC interface, including merged stat
counters, txn entries, response cache entries, time series data,
and other system-local data.

After some thought, Matt and I ruled out the possibility of not
inlining the value and just using a single version--not much more
efficient and would allow us to use the MVCC code exactly as is.
However, this would have made merging difficult, as there would be
no way to create the MVCC metadata on the first merge.

Support for both types of values is becoming increasingly unwieldy
and the prospect of a parallel interface for querying time series
data and the bifurcation of different regions of the map to be
"mvcc" and "non-mvcc" seems like a pandora's box of troubles.

Follow-on commits in this branch will implement the actual inline
value in proto.MVCCMetadata and the corresponding improvements to
mvcc.go. I intend to take this opportunity to substantially improve
the performance of mvcc scan.
Merge pull request #180 from cockroachdb/spencerkimball/inline-mvcc

Remove all instances in test code which use a zero timestamp.