#4 Lovely loop in ModelMapping

[Anonymous]

If you specify a collection element-type that is not
defined anywhere in the .jdo file, and if you do not
specify a table (letting xorm resolve it as the table of
the element-type), ModelMapping will loop infinitely.

I broke this when I added the "enhancement" of not
requiring the table to be explicit. Gotta add some sort
of looping protection there or change the way the
mapping file is processed.