In `bp_core_activation_notice()` do not show notices in two new circumstances:

* Viewing network admin, and BuddyPress is not network activated.
* Viewing user admin.

This prevents BuddyPress's admin notices from leaking into administration areas where the messages are not relevant, and are likely to clutter up the admin interface.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7670 cdf35c40-ae34-48e0-9cc9-0c9da1808c22