Autocomplete as POST request

Hi boonebgorges-

I was running into a problem where in certain cases in nested groups (I'm using BP Group Hierarchy), the autosuggest GET request to `admin-ajax.php` was returning a 302. Eventually, I realized that the `_wp_http_referer` value was really long in the cases where I was seeing a 302. Like 180 characters and more, from long group names coupled with the group hierarchy url structure. I've switched the request over to a POST instead, and it seems to be working in those cases.