Flow fix

[Caruychen]

The flow_edge functions:

• edge_has_residual_capacity_to
• edge_augment_flow_to

Have been updated to update the origin node's is_free and is_via_augment states. This should deal with the issue where path finding lands on a node that is already taken by another path. Prevents overlapping paths.

Side note, there are memory leaks from the "parser" unit tests that need to be fixed.

[crl-n]

Great work! The changes work with my version of the solver (tested with subject3.map) with minimal changes to the solver code.