Unit tests for bp_activity_post_update()

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8521 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Don't use extract() in bp_activity_post_update()

See #5698

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8522 cdf35c40-ae34-48e0-9cc9-0c9da1808c22