Update CLIClient to track the last error code recieved and return that
as an exit code if the last command fails
Ensure the Dump/Load clients return non-zero error code if the Dump/Load
fails.
Ensure lastError doesn't exceed 255. 

Remove static variable in favor of return codes.
merge tjoneslo: Exit code on command

Merge pull request #54 from FoundationDB/sql-layer-client-tools/exit-code-on-command
https://github.com/FoundationDB/sql-layer-client-tools/pull/54