Estimated hours taken: 0.5
I moved the scripts bootcheck, binary, binary_step, divide and assemble
into the tools subdirectory from the main mercury directory.
I also added the auxiliary scripts appears, cleanint and half.
I modified binary and binary_step to compare stage3 with stage2.ok,
and only pass a stage2 compiler if the comparison finds no differences.
This requires that the Mmake.params files be copied, not linked, from
the top level's Mmake.stage2.params. The old behavior (no comparison)
is still available; just specify -c (compile-only).