Implement isAlive?() on Unix. Closes #661.
Implement isAlive?() on Unix. Closes #661.

marcusnaslund/rock,fredrikbryntesson/rock,cogneco/rock,thomasfanell/rock,magic-lang/rock,zhaihj/rock,ds84182/rock,marcusnaslund/rock,jonathanudd/rock,fredrikbryntesson/rock,fasterthanlime/rock,shamanas/rock,davidhesselbom/rock,shamanas/rock,ooc-lang/rock,magic-lang/rock,thomasfanell/rock,jonathanudd/rock,cogneco/rock,fasterthanlime/rock,davidhesselbom/rock,zhaihj/rock,ooc-lang/rock,kirbyfan64/rock,ds84182/rock,kirbyfan64/rock