Members: when signing up a new user, use our `bp_update_user_meta` wrapper function to store the `activation_key` in usermeta.

Fixes #5884, props Clean-Cole

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9197 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
User Settings: fix PHP notice when changing your email address.

Fixes #5982, props slaFFik

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9198 cdf35c40-ae34-48e0-9cc9-0c9da1808c22