Disable OpenMP

## WHY
performance in multi core machine.

![i-a15662b8___datadog](https://cloud.githubusercontent.com/assets/261700/5483196/7d05118a-86b1-11e4-983e-f3706bb2361b.png)

Disable OpenMP

![i-a65662bf___datadog](https://cloud.githubusercontent.com/assets/261700/5483198/82ac60d4-86b1-11e4-9fdd-35b73dd4a2e3.png)



## TODO

* [x] add graph for CPU usage to compare

## REF

* [Parallel Execution With OpenMP](http://www.imagemagick.org/script/openmp.php)