Added distance to prevent unintended reordering

Added a small distance delay on the sortable to prevent users from unintended
triggering of the reordering. (Happens all the time i'm using slickgrid).
i.e. the users tries to sort the column but fails since his mouse was still
on the move a little bit and 1px is enough to trigger reordeing here.
Please try, it still feels very responsive.
Replace 'hover' deprecated pseudo-event

'hover' pseudo-event has been deprecated in jQuery 1.9.0,
use of 'mouseenter' and 'mouseleave' instead.
Merge pull request #519 from loris/patch-1

Replace 'hover' deprecated pseudo-event
Changed distance value
Merge pull request #517 from ckosmowski/master

Add the distance delay to the header drag code.
Fix #520 - dropstart event not firing
Use of navigator.userAgent instead of $.browser

$.browser object has been removed from jQuery 1.9.0
Merge pull request #521 from loris/patch-1

Use of navigator.userAgent instead of $.browser
Added distance for dragging rows

Added distance to prevent users from unintended dragging of rows.
Merge pull request #523 from ckosmowski/master

Distance for dragging