PortalGun has been rewritten, 1.4.5v1 is identical in terms of functionality to 1.4.6v1.
There is no documentation on the rewrite at this point of time so use at your own discretion.
Some stuff has been shifted around, it is NOT compatible with the old versions, most of the items can be carried over however. A few recipes has been changed as well.
I am not liable for any crashes/corruption that happens to your worlds when updating.