Measures reported by XchgCatQueueTest

The XchgCatQueueTest indicates how well SMTP is processing LDAP lookups against the global catalog servers. The Exchange Categorizer queue length should be around zero unless the server is expanding distribution lists. While expanding distribution lists, this counter can occasionally go up higher. This is an excellent measure of how healthy the global catalogs are. If there are slow global catalogs, this queue length will increase.