Aui 1122 dragn drop between columns

Hi Iliyan.

Due a problem with the css styles, the heights of colums divs are not correct.

This fix checks if the dropNode is a column. If it is, then the fix changes the calculation and sets the region.bottom to the bottom of the last node of the column.

Another problem is that this code is portal-dependant. If you have any doubt, please ask me.