added ability to specify from cli when generating a model/migration whether particular property should be an index like this 'rails g model person name:string:index profile:string'

Otherwise, the schema and seed will be loaded onto the
test database.

Delete unnecessary line that was necessary before I changed the code and it became no longer necessary.

Testing Sandbox removed.

added failing tests for has_many, has_one and belongs_to associations with strict mass assignment sanitizer, fixed build_record to not merge creation_attributes, removed failing nested attributes tests (that feature was broken anyway) #4051

  from Ruby stdlib.

This is mostly the same as 876bade5
that was reverted due to test failures, but now with a correction.

This reverts commit a0edfb4d, reversing
changes made to 4012fcff.