Fix help system build under Moscow ML given removal of 2.01 support

Allow Moscow ML build to happen using (as yet unreleased) v2.10.

Basic strategy is to make adoption of basis 2002 even more
thorough. In particular, the Timer structure is now as per
the 2002 Basis.

It is possible to detect that one is working with Moscow ML 2.10 or
later by checking the Holmakefile variable $(HAVE_BASIS2002), which is
set (to value "1") when in 2.10 or later. It is unset elsewhere. See
an example of its use in help/src-sml/Holmakefile.

I do need to be explicit about dependencies where the Holmakefile
takes over from Holmake's builtin handling of file construction. So,
there need to be some mentions of basis2002.uo in
help/src-sml/Holmakefile.

Start to implement the Basis 97 extensions that Moscow ML hasn't got
in order to force our codebase to get up-to-date. It should also
mean less bodging around for the Poly/ML code. I haven't checked that
my changes to tools-poly/poly/poly-init2.ML have done all that is
required yet. Feel free to fix problems arising there (I hope it will
just be a matter of deleting things).

Fix error in dependency information in help/src-sml's Holmakefile.

Use $(protect ...) to protect the spaces that might occur in the $(SIGOBJ) filename on Windows. This allows this directory to build properly.

Get the 'flashy' incremental percentages effect to be turned off in
situations where there is no TERM variable set. Also, properly record
the Doc2Txt and Doc2Tex executables' dependency on Flash.uo.

It turns out that Scott's Help DB is not compatible with Moscow ML's
own, so I have to compile Moscow ML's original code to get the Moscow
ML database to work. I put that code into MyDatabase and faff some
more with the Holmakefile. The Database code is deleted in help/src.

Make this directory build Moscow ML versions of the help executables,
promoting Scott's PolyML version of Database to be the primary
version. In general, take the attitude that PolyML sources here can
be primary, and that the Moscow ML stuff can be made to work with
appropriate use of My* structures, and Holmakefile magic.
When this is confirmed to work (really just need to test makebase),
I will remove help/src entirely.

Tidying the PolyML help stuff.

Got the help build system working on PolyML.

Start working on porting the doc building system to SML (i.e., not Moscow ML)
to get it working with Poly ML.