Fix constraint and Cypher handling

[j6k4m8]

This fixes a few places where constraints could get mangled on their way from the parser to an executor.

• keeps multiple dynamic edge comparisons as separate triples instead of flattening them together
• makes both NetworkX and Neo4j evaluate every dynamic edge comparison
• escapes Cypher values instead of dropping raw strings into the query
• gives parallel motif relationships distinct Cypher variables while leaving the usual single-edge names alone