xProfile: correctly sanitise `$_POST['field_ids']` when a user updates their profile.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7889 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Merge branch 'master' into xprofile-types

Conflicts:
	bp-xprofile/bp-xprofile-screens.php