use a real object for files instead of a tuple
unique urls for files, logs and render results (just missing the proper mime type for exr files)
fix bug with slaves not getting the correct machine name
Support for fluid files and better support for point cache (including external cache for particles)
This also fixes a couple of bugs with frame based dependencies and with file transfer.
NOTE: With external point cache and fluids, the path needs to be relative or relative to the file (starting with //) if the files are not on a shared drive. It should eventually warn if that is not the case, but doesn't right now, so be careful.
