Print Warning if relations points to receiving endpoint target
Receiving nodes are overridden, once a new message is received. If the replaced node hade relations pointing into it (or nodes in its subtree), those relations are not updated. Thus, they point to nodes not contained in the tree anymore. This must be avoided.
When encountering such a situation when running the RagConnect compiler, a warning should be issued.
As a next/future step, an attribute could be generated in addition, to check at runtime, if currently any relations are pointing in a (or any) receiving endpoint target(s).