Handle change_column error when column has default binding or indexes.

Tests for #455.
these tests were only meant for MS-SQL
Return early if table name is nil
we should first allow super AbstractAdapter to initialize then extend spec

otherwise using *adapter: jdbc* configuration might no work (fixes #457)
test that we allow `nil` to be passed into `table_exists?` (details at #460)
use the maven released postgresql driver as dependency for IDEs
Merge branch 'master' into jruby-head

* master:
  use the maven released postgresql driver as dependency for IDEs
  test that we allow `nil` to be passed into `table_exists?` (details at #460)
  we should first allow super AbstractAdapter to initialize then extend spec
  Return early if table name is nil
  these tests were only meant for MS-SQL
  Handle change_column error when column has default binding or indexes.