Performance Improvements - Create a fast timer class which can be used to replace gettimeofday() and time() for Drizzle

Please see Mark Callaghan's work on fast timer creation for the MySQL@Facebook branch, specifically this revision: http://bazaar.launchpad.net/~mysqlatfacebook/mysqlatfacebook/trunk/revision/71 We should encapsulate this into a class in /drizzled/ and begin using it in performance-intensive areas.