Compatibility for ActiveRecord 4.x

Fixed issue with empty arguments being passed into joins() and a change
in ActiveRecord::Reflection::AssociationReflection in 4.x.

ActiveRecord requirements upgraded to >= 3.2 in gemspec.

Maintained compatability with ActiveRecord 3.2.x
Use appraisal to run suite on ar4
Merge branch 'master' of git://github.com/t27duck/ar_outer_joins into t27duck-master

Conflicts:
	ar_outer_join.gemspec
Remove deprecation warnings under AR4