fixed regression for aliased tables in 0.3.1

assumption that all the tables have _autoincrement_column attribute
isn't correct.
Also added a test case for it.
documentation fix: typ instead of type

Documentation incorrectly suggested using 'type' key for specifying
colander type in the model.
Colander actually uses 'typ' (probably to avoid name collision with
type builtin).
Merge pull request #50 from hadara/master

fix for aliased models (regression in 0.3.1)