some marshal-ing tests (in an attemt to reproduce #573 without luck)
move around schema tests + remove duplicate test_current_schema
[postgresql] align with (backport) Rails distict white-space fix (regression in 4.0.10)

https://github.com/rails/rails/issues/16623
[postgres] user defined types should not raise an error 

backport from https://github.com/rails/rails/commit/b1cae7351a0ed5a3
[postgres] adapter was missing the custom rename_index method (fixes #577)