Resolve issue where default_scope attributes were conflicting with imported columns. DO NOT import default scope values as that defies intuition since they're not typically used to populate default field values.

[#78]
Re-arrange the order of checking for the primary key to issue a 
"prefetch_primary_key?" before trying to generate it from sequence_name. This resolves an issue with postgresql adapter blowing up when a primary key can't be fetched.

[#78]
Merge branch '78_default_scope_issue'