find_or_create_by_x with create params via association broke in 2.3.9

Sorry about opening this bug - I'd prefer to re-open #1108 but I don't know how to do that.

The fix to #1108 added two new bugs.

Commit fad166c15277c72b370c90e890d509d0f6c9af63 (i.e. 2.3.9) broke find_or_create_by_x with additional parameters for the create, when called through an association. Since http://dev.rubyonrails.org/ticket/7368 you've been able to pass additional parameters that are ignored by the find but used by the create. fad166c broke that behavior.

fad166c also broke find_or_create_by_x with a block provided. It used to yield to the block but it doesn't anymore.

For more info please see my comments to #1108.

For convenience I'll attach the patch to this report, too.