Use the instrumentation framework to instrument Strong Params
Deprecate #connection in favour of accessing it via the class

This allows end-users to have a `connection` method on their models
without clashing with ActiveRecord internals.
Fix race condition in test

This should fix travis. For real this time! This is the one!

The readpartial(100) meant that an earlier assert_stdout could chomp up
the output that a later assert_stdout wants, meaning that the later
assertion fails.

Reading only 1 byte at a time ensure that we don't read any more than is
necessary to verify the assertion.
Merge pull request #9626 from dasch/dasch/instrument-strong-params

Use AS::Notifications to instrument Strong Params
Merge pull request #9371 from benmoss/access-connection-via-class

Access an instance's connection via its class, rather than via #connection
Uniqueness validation uses a proc to specify the `:conditions` option.

This is a follow up to #5321 and follows the general direction in
AR to make things lazy evaluated.