pending changes in grid.base.js

Hello Tony,

the pull request contains the last suggestion which I posted last time in [the jqGrid forum of trirand](http://www.trirand.com/blog/?page_id=393). I described the changes in the corresponding commits additionally to the text in the forum. The changes near `beforeSelectRow` looks more as it be because of removing `if` and moving the code in the body of `if` one tab left.

Best regards
Oleg