attempts associations

This commit tries to implement associations, but it doesn't work. It
seems like the problem is that the lambda that's supposed to fetch the
associated models has its scope set when it's defined in SqlObject
rather than when it's called? To wit:

 19  	def show(parameters):
 20  	    post = Post.find(Post.cxn, "posts", parameters["id"])
 21  	    #trying to debug associations
 22  	    debug()
 23  ->	    post.author()
[...]
(Pdb) s
--Call--
>
/home/zmd/Code/Wires/serpentine_record/serpentine_record.py(107)<lambda>()
-> search = lambda: eval(class_name).find_where({primary_key:
self.__dict__[foreign_key]})
(Pdb) class_name
'User'
(Pdb) eval(class_name)
*** NameError: name 'User' is not defined
[...]
(Pdb) globals().keys()
dict_keys(['__cached__', 'MassObject', 'SqlObject', '__name__',
'sqlite3', '__loader__', '__doc__', '__package__', 'debug',
'__initializing__', '__file__', '__builtins__'])