This will allow legacy externals like iemmatrix and zexy to properly load
aliases the first time when the user instantiates an object with
[namespace_prefix/alias_name]

This becomes relevant when there are kludge classes that essentially just
"#include" the original C file of a class and add an alias_setup function
which just calls the original setup routine. (For example, see iemmatrix.)
However, such an approach still calls class_new with the original class name.
Thus "namespace_prefix/classname" gets added to the pd_objectcreator
methodspace, but "namespace_prefix/alias_name"-- which is what we want--
does not. This results in a series of 1000 recursive calls into
pd_objectmaker's new_anything method. (I.e., sys_load_lib finds the
"namespace_prefix/classname" is already loaded, new_anything_sends a
typedmess to pd_objectmaker's new_anything method, which calls
sys_load_lib, etc.)

To prevent this, we just make sure to add "namespace_prefix/alias" by
adding the relevant lines to class_addcreator. This should really be
happening anyway-- since internal classes don't have a class_loadsym
they aren't affected, and externals with aliases won't work with
namespace prefix without this.