More robust checks before checking module inclusion
More robust checks before checking module inclusion

Specs for in_memory and yaml still fail, but at
least they're running now. Previously they bailed
out immediately because of calling [] (lambda.call)
on nil.

This (like many other dm-migrations specs) looks
kinda weird and will probably be refactored soonish
datamapper/dm-migrations,avillagran/dm-migrations