Update grid.formedit.js

We get simple and direct information about the grid: id. It allows to call different jqGrid methods (like `$.jgrid.createEl` or `$.jgrid.checkValues`) with `this` initialized to DOM of grid.
Update grid.filter.js

forward DOM of grid to `$.jgrid.createEl`, `$.jgrid.checkValues`, `$.jgrid.bindEv` and to `searchoptions.custom_value` and `searchrules` defined as functions.
Merge pull request #450 from OlegKi/master

fix bug in search validation and forward correct "this"