Canned algorithms in libgalois leave changes in the PropertyFileGraph when they fail

[arthurp]

Leaving the property on the PropertyFileGraph will: a) force a rerun of the algorithm to use a different property name to avoid conflicts, b) waste memory since the old property is referenced and will hang around in memory. These are both issue in a Jupyter notebook where having a failure in a given cell is usually handled by only rerunning that one cell.

I think a good option is adding a rollback (delete the new property) if the algorithm fails. Another options would be to chang the property creation semantics of algorithms to be "add or overwrite", but I think that could make it easy to accidentally destroy your data due to the silent overwrite.

This originally came up in #5 (comment).

[arthurp]

Fixing this should be a relatively straightforward matter. Many algorithms already have a thin wrapper function that could easily be modified to check for a returned error and delete the output property if it exists. Other algorithms could have such a thin wrapper added if they have a large number of returns making removing the property in every care messy.