fixed incorrect setting default

`enforce_uniqueness_on_sti_class` should be `enforce_uniqueness_on_sti_base_class`
Merge pull request #155 from deadlyicon/patch-1

fixed incorrect setting default
Version bump to 2.4.2
Regenerate gemspec for version 2.4.2
Merge pull request #156 from futhr/master

fix test that original contr. decided to comment out for no apparent reason