integrate experimental-optimize-jit branch into project-optimize-jit branch

Opening a feature request in the tracker to have more visibility into the help wanted for getting the JIT improvements from our CGO 2015 paper (https://dl.acm.org/citation.cfm?id=2738610) into the master DR branch. Please see https://github.com/DynamoRIO/dynamorio/wiki/JIT-Optimization for more details.