Use a more canonical method for populating scipy's sparse matrices

[wd15]

At present we seen to be creating a new temporary matrix in order to add new entries to a current matrix.

trunk/fipy/matrices/scipyMatrix.py@5232#L195

Scipy can now store the i, j, value (COO matrix) arrays as a sparse matrix format. It deals with double entries and repeated array additions. We can then convert to a different format for the solve step.

See explanation in http://thread.gmane.org/gmane.comp.python.scientific.user/31754.

Imported from trac ticket #443, created by wd15 on 05-15-2012 at 10:09, last modified: 05-15-2012 at 10:10