refactoring insert_diagonal so that it can add or overwrite the diagonal weights
refactoring insert_diagonal so that it can add or overwrite the diagonal weights
google-code-export/pysal,pombreda/pysal,google-code-export/pysal,google-code-export/pysal,pombreda/pysal,pombreda/pysal,google-code-export/pysal,pombreda/pysal