The great includes migration of 2019 (autotools)

The great includes migration of 2019 (autotools)

Ok - so one of the steps in building CDE is an early phase called the
includes phase (make includes).  At this point, all of the public
header files are exported to exports/include/Dt, DtI, ...

Then, the software is built using that include dir.

This of course does not work in autotools.  Much of the software does
things like #include <Dt/something.h>, so in order for the build to
succeed, this behavior must be represented/replicated in some way.

It seems the usual way of dealing with this is to place all public
headers (and in some projects, ALL headers) into a toplevel include
directory.

We now do this for all public headers - they have been moved from
wherever they were and placed in the appropriate spot in includes/

This will break the Imake 'make includes' phase unless the Imakefiles
are fixed (remove the HEADERS = stuff, and the incdir defines).  This
has not been done at this point since in reality, once autotools works
properly, there will be no need for the Imake stuff anymore, and I
intend to get rid of it.

This is just a warning for now - Imake builds in this tree will now
fail at the 'includes' stage.

This commit is only the migration.  In upcoming commits, libtt will be
fixed so that the hack being used before to get around this problem is
removed as there will no longer be any need.

And then the autotools work continues...