Fix for #615,

Replaced event.clientX with event.pageX in the dragStart and dragMove functions
Update grid.base.js

fixed: if the addRowData's rdata parameter is array and pos is 'after' or 'before', then can't work
fixing exception in setting floating on undefined

One need use `.data("uiSortable")` instead of `.data("sortable")` in the current version of jQuery UI. The current code produces exception during the attempt to assign `floating` property on `undefined` object.

The exception will be catches for example in [the line](https://github.com/tonytomov/jqGrid/blob/v4.6.0/js/grid.base.js#L2661-L2663) of jqGrid code

    try {
        $(ts).jqGrid("sortableColumns", thr);
    } catch (e){}

but not in case of direct usage of `sortableColumns`. The method end always with exception and so the usage of `try {...} } catch (e){}` is really required in all usages of the current version of `sortableColumns` together with the current versions of jQuery UI.

The suggested fix should work on old and new versions of jQuery UI.
Merge pull request #617 from shenghe/master

Update grid.base.js
Merge pull request #618 from OlegKi/master

fixing exception at the end of sortableColumns
Merge pull request #615 from danielpetroianu/master

Column resize indicator is misaligned when the grid is too big so that you have bowser horizontal scroll
Fix select all checkboxes to skip the jqgroup row when grouping and multiselect are on
Fix frozen column scrolling when footer row is enabled
Fix show correct summary value when group summary pos is header.
Fix show correct group when showSummaryOnHide is on and minus icon is clicked - i.e collapse group