Get Holmake to compile under Moscow ML again

Let Holmakefiles pass on a --dbg flag if it was passed to Holmake

The standard variable environment that is consulted and updated in a
Holmakefile now starts with

DEBUG_FLAG |-> --dbg

if --dbg was passed to Holmake.

Fix mosml Holmake given changes in logging branch

Replace 'print' with Holmake's output functions

Make KERNELID var get its proper value in Holmake

Issue was that Poly/ML evaluates many things at compile time rather than
run-time.

Move mosml Interrupt magic to mosml_Holmake.sml

Give HM_BaseEnv a signature

Move mosml Interrupt magic to mosml directory

Purge Holmake.sml of much Moscow ML specific code

The Moscow ML stuff has moved into mosml/BuildCommand etc

Progress with github issue #77