Activity fixes

[r-a-y]

Hi Boone,

This pull request addresses:

• 25 - Multiple activity entries generated when editing a groupblog post

And two other things:

• 621c6e7 - Add activity comment check for groupblog posts
• 2ff649d - Use post permalink for groupblog post activity permalink

Let me know if you have any Qs!

[boonebgorges]

Awesome, thanks @r-a-y ! I've merged into the 1.8.x branch.