Add option driftInitialLocations.
Add option driftInitialLocations.

This option will drift initial virus and serum locations be the degree specified times the year difference from the initial virus.  Defaults to 0.0.  This is sometimes necessary to prevent "tangled" maps that don't converge.
luminwin/beast-mcmc,luminwin/beast-mcmc,luminwin/beast-mcmc,luminwin/beast-mcmc,luminwin/beast-mcmc