Base CSS uses wrong class names

In the migration from a previous version of Panels to 6.x-3.9 the nomenclature for Flexible Panels changed from .panel-flexible- to .panels-flexible- in the code, but the base CSS provided with the panels module still has the old .panel-flexible- class name specified. As a result, certain styles are not applied to our panels that used to be.

Same for .panel-region-separator {} - this was originally .panel-separator and in 6.x-3.9 it changed to .panel-region-separator, and the margin-bottom: 1em; is not applied to the new class name.

May be other base style definitions lost in the migration of class names to 6.x-3.9 as well. These are the few that jumped out at us on our website