Add parser-specific tests

tests/parser/aggreg.py

+#!/usr/bin/env python
+
+import opengeode
+y=opengeode.ogParser.parser_init(string='''state ENTRYA;
+          substructure
+            procedure entry EXTERNAL;
+          endsubstructure ENTRYA;''')
+
+y.composite_state_body()
+
+z=opengeode.ogParser.parser_init(string='''state CHECKING;
+        substructure
+          state ENTRYA;
+          substructure
+            procedure entry EXTERNAL;
+          endsubstructure ENTRYA;
+        endsubstructure CHECKING;
+''')
+
+z.composite_state()