Manage Group page is slow if you have smart groups

This seems to be a regression caused by CRM-20226. Previously group counts were calculated via SQLstatements that explicitly counted records in the civicrm_group_contact and civicrm_group_contact_cache tables.

However, with CRM-20226, this behavior was changed and instead they are being counted via the Contact.getcount API call which seems to trigger a group cache rebuild.

(Mentioning Manage Groups (plural) to aid searching, as this didn't come up in a search for "manage groups count" - Dave J.)