If the blk of a default rectangular array is 1, don't multiply it by the index.
Merge pull request #1030 from benharsh/blk-one-shortcut

Potential indexing performance improvement for DefaultRectangular

This change was observed to have performance improvements for the CSU Jacobi code with gcc4.7 at both large and small problem sizes. Chapel was competitive with the reference version up to "-O2", but at "-O3" the reference version pulled ahead. This change brings Chapel much closer to the CSU OMP reference version at "-O3".

This change passed parallel testing for a single node.

I have not measured other performance benchmarks yet to look for an improvement. We will inspect the results of the nightly performance run to determine whether or not this is a change we should keep in the long term.

This patch was reviewed offline by @bradcray.