JRuby Regression Update

Fixes a regression introduced for schema dumping feature in >0.70 via     https://github.com/engageis/activerecord-postgres-hstore/commit/ca34391c776949c13d561870067ddf581f0561b9#lib/activerecord-postgres-hstore/activerecord.rb

I updated the PostgreSQLColumn and PostgreSQLAdapter classes to be compatible with JRuby like it was prior to 0.70.  Please let me know if you have any questions or comments.