Only register 'new_blog' activity action on multisite installs.

Fixes #4980.  Props imath.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7076 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Only register legacy forum activity actions if the legacy forums are active.

Fixes #4979.  Props imath.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7077 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
POT, generated from r7077

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7078 cdf35c40-ae34-48e0-9cc9-0c9da1808c22