Make interactive HOL recursively read INCLUDES to augment loadPath

Closes #604

Make polyscripter tool pay attention to Holmakefile INCLUDES line

Refactor some code along the way so that this reading of Holmakefiles
is now a standard facility in the ReadHMF structure.

Test that it works by making the polyscripter test read from
examples/misc.

Read .holpath directories to allow relocatable developments

If there is a .holpath file in a directory containing a string with a
name for the development under that directory, then the object
files (.uo and .ui) in that directory will be easily relocatable
because they won't use absolute paths, but will instead use
$(devname)/ type paths.

Multiple developments can combine in this way, and there is additional
machinery to make sure that all of the relevant directories are
scanned before reading and writing of object files happens.

Get mosml Holmake to build with new Holmake_types.

Rework lexing of Holmakefiles so that the system doesn't choke on
Joe's monster example. The result is simpler code (which is a bit
worrying in itself), and one less dependency on mosmllex. It
successfully reads all of the distribution's makefiles, as well as
Joe's.