re-adding the loading of message catalog files on server startup. Since loading is only done at package install if acs-lang is already installed and this is not necessarily always the case
cleanup and renaming of import/export procs in lang::catalog namespace. Now there are really only two public procs to know about: lang::catalog::import and lang::catalog::export. Updating all invocations of the procs and test cases. Adding proc lang::message::unregister for deleting message keys - used in test case teardown.