Improving performance of loading large local grids

I described the problem in [the bug report](http://www.trirand.com/blog/?page_id=393/bugs/improving-performance-of-loading-local-data-in-jqgrid) and [the answer](http://stackoverflow.com/a/25532422/315935).
Merge pull request #635 from OlegKi/master

Improving performance of loading large local grids