NotSerializableException for SPOAccessPath

[thompsonbry]

java.io.NotSerializableException? in dawg-triple-pattern-003.

The query is just a scan for

(?a,?a,?b)

[thompsonbry]

The SameVariableConstraint? was being attached to the AccessPath? by an inline TupleFilter? subclass. This was causing the SPOAccessPath reference to be dragged in, which resulted in the not serializable exception.

A top-level SameVariableConstraintTupleFilter? class was created to replace the inline class. The AccessPath? constructor was modified to use this top-level class and thus avoid dragging in the AccessPath? instance when the filter is serialized.

This issue was observed in the development branch (TERMS_REFACTOR_BRANCH). However, it seems likely that the same exception could appear in the 1.0.x release.

The changes were applied to both the 1.0.x maintenance branch and the development branch.

Committed revision r5234.

[thompsonbry]

Fix verified against the dev-branch.