The method, as stated by its comment, is supposed to answer the number
of bytes actually transferred from the file-system.  In fact, it
answers the size of the String input into the method.

Magma won't even come close to running in the trunk image with this
problem.  StandardFileStream>>#readInto:startingAt:count: is breaking
its contract.

Nicolas and/or Levente, can you help?  These recent changes you made
appear to be an optimization of FileStream?

Thanks,
  Chris