Updated FindSimbody.cmake to work properly for 64 bit Windows installations.
MobilizedBody::isSameMobilizedBody() is supposed to compare two MobilizedBody handles to see if they both point to the same implementation object. Instead, it was comparing the handle addresses so only returns true if they are the same handles, leading to false negatives when a handle is used as a reference to an object owned elsewhere.

Fixes GitHub issue #15.
Merge pull request #16 from sherm1/master

Two small fixes: FindSimbody now works for 64 bit Windows; MobilizedBody::isSameMobilizedBody() fixed.