Fix random number synchronization in randomChoice.
Fix random number synchronization in randomChoice.

Switch nextDouble() from base random.nextDouble() to MathUtils.nextDouble() that synchronizes random number seed across threads.  Patch via Connor McCoy (cmccoy at fhcrc.org).
evolvedmicrobe/beast-mcmc,danieljue/beast-mcmc,evolvedmicrobe/beast-mcmc,evolvedmicrobe/beast-mcmc,evolvedmicrobe/beast-mcmc,danieljue/beast-mcmc,danieljue/beast-mcmc,evolvedmicrobe/beast-mcmc,danieljue/beast-mcmc,danieljue/beast-mcmc