Added DB transaction wrappers.

md5sum a.out
dfbb90624ebdf83db10a50f138c0078c  a.out

Added start, abort, and end transaction wrappers for the mySQL
connection object. Intent is to use them to back out of a heatmap PUT
that had faulty data.

The current spaghetti code in the PUT request makes deciding how to
handle that particular case more difficult though.