Exit after saving component settings in Dashboard

Allowing the PHP process to continue after wp_redirect() resulted in
background fatal errors, as components attempted to initialize based on
active_components information that did not properly match the libraries that
had actually been loaded. Plus it wastes CPU cycles.

Fixes #5506

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8230 cdf35c40-ae34-48e0-9cc9-0c9da1808c22