Begin the process of eliminating the name clash between the VM's assert() macro and the standard (<assert.h> / <cassert>) assert() macro.

This first step is to rename assert() to vmassert(), but continue to provide an assert() synonym for backward compatibility. This renaming should be back-ported to earlier versions, to simplify backporting of other changes.

Once this change and the associated back-porting has been completed, we can incrementally change uses of assert => vmassert in the latest development trees. Once that renaming has been completed, we can remove the backward compatibility synonym from the latest development trees.