Convert all path-related (body, switch) logic to use integer milliseconds

Convert all path-related (body, switch) logic to use integer milliseconds

This is an experimental change, so keep an eye out for problems.  It
will almost certainly break maps that expect higher time granularity
than 1 millisecond (0.001 second), any such maps will need to be fixed
manually.

git-svn-id: https://s.snth.net/svn/neverball/trunk@3454 78b8d119-cf0a-0410-b17c-f493084dd1d7