Add a 'realclean' phony target which removes all objects files and
libraries from the dso/config folder that belong to the egs++ library
including sources and geometries. Useful when one wants to recompile the
full library.

The 'clean' target only removes object files in the egs++ folder without
cleaning objects for geometries, sources, etc. It is meant to only
rebuild the basic part of egs++.

Note that libiaea_phsp.so (iaea_phsp.lib on Windows) is preserved.

Fix the 'realclean' target for guis as well, to make it general for
Linux and Windows and use the proper Makefile name.

Also expand the 'clean' rule in the iaea_phsp makefile to remove all
object files.

- Call target 'realclean' for egs++
- Build only geometry, shapes and ausgab objects in 'egspp' target:
  those are the only ones needed for egs_view
- Remove iaea_phsp dependency from 'egspp' target
- Remove variable 'cleanup'
- Add comments

- Add call to 'realclean' egspp
- Use 'realclean' for egs_view
- Updated output message to reflect library cleaning

- builds only geometry, shapes and ausgab objects as those are the only
  ones needed for egs_view
- Removed iaea_phsp build
- Add variable the_config

Define the variable the_config in windows makefiles, allowing the use of
an existing configuration. Previously, this was hard-coded in the build
paths as win-static.

Set the gui_make command name to the make utility used during the
configuration, which is available in the configuration file via the
variable make_prog.