ENH: Updating SimpelITK version to 0.7.0.dev54

This update to SimpleITK includes the following:
 Fix for mantis 3157
 Improved compilation time with parallelism
 Improved VS9 compiler check
 Windows numpy size conversions fix

Additional tweaks to external file include:
 Adding cmake flag to remove git hash for version.
 Adding cmake variables for git tag and url.