Make Variable class private, and rename base-class get_read_node to _mark_reading

- this solves type issues with RPython and is also more clear, because the super call for get_read_node was never nice to begin with.

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Conflicts:
	src/som/compiler/variable.py
Added assertion about SourceSection of Node

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Extracted helper method _get_source_section for direct use, to avoid setter after construction

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Conflicts:
	src/som/compiler/parser.py
Added proper error for unresolved super classes during parsing

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added proper error when integer parsing fails.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Extended parser to allow 'primitive' as identifier

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Conflicts:
	src/som/compiler/parser.py
Fixed argument processing for DNU, number of arguments includes self, which is not desired here

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Conflicts:
	src/som/vmobjects/abstract_object.py
Output error immediately and quit.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Universe.load_class has to set the global to ensure that classes are loaded only once [TODO: ensure in all SOMs!]

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Fix has_primitives to also check on the class side

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Fixed typo

- no idea why that wasn't found by RPython, and where it is coming from

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Implemented missing #instVarNamed: primitive

Signed-off-by: Stefan Marr <git@stefan-marr.de>

Conflicts:
	src/som/primitives/object_primitives.py