Ensure HOL4 works with fixed-width integers under Poly/ML.

Integers under Poly/ML 5.6.1 are likely to be fixed-width by default (up until now they've always been arbitrary precision). Some changes were needed to cope with this:

- The Arbint and Artbnum structures effectively assumed Int.int = IntInf.int.
- The Standard ML structure Time is based on LargeInt.int and not Int.int. Code for printing times has been re-implemented using the Date structure.
- The smart-configure.sml file used the Overflow exception to distinguish between Moscow ML and Poly/ML. This test is now based on a difference in the printing of General.Fail exceptions.

Removed trailing whitespace from all .sml and .sig files.

This affects over 900 files and was done using emacs's delete-trailing-whitespace
function in batch mode. Building the system with Poly/ML and Moscow ML seems to
work, so I'm hoping these changes don't break anything. Please complain if
they do!

PolyML compatibility. See tools-poly/README.