fix missing require for pp in 546de0f
fix missing require for pp in 546de0f

This fixes errors in the isolated active record tests such as:

```
Error:
RelationTest#test_already-loaded_relations_don't_perform_a_new_query_in_#pretty_print:
NameError: uninitialized constant RelationTest::PP

      PP.pp relation, StringIO.new # avoid outputting.
      ^^
    test/cases/relations_test.rb:2049:in `block (2 levels) in <class:RelationTest>'
    /rails/activerecord/test/cases/test_case.rb:54:in `assert_queries'
    /rails/activerecord/test/cases/test_case.rb:67:in `assert_no_queries'
    test/cases/relations_test.rb:2048:in `block in <class:RelationTest>'
```

yawboakye/rails,georgeclaghorn/rails,georgeclaghorn/rails,yahonda/rails,kmcphillips/rails,kddeisz/rails,Edouard-chin/rails,Edouard-chin/rails,MSP-Greg/rails,yawboakye/rails,MSP-Greg/rails,BlakeWilliams/rails,yawboakye/rails,kmcphillips/rails,kmcphillips/rails,BlakeWilliams/rails,yawboakye/rails,Erol/rails,kmcphillips/rails,esparta/rails,Erol/rails,rails/rails,rails/rails,Edouard-chin/rails,esparta/rails,Edouard-chin/rails,yahonda/rails,georgeclaghorn/rails,kddeisz/rails,kddeisz/rails,rails/rails,esparta/rails,BlakeWilliams/rails,MSP-Greg/rails,georgeclaghorn/rails,esparta/rails,yahonda/rails,yahonda/rails,Erol/rails,kddeisz/rails,BlakeWilliams/rails,MSP-Greg/rails,Erol/rails,rails/rails