Fixes skipping object callback filters

This allows you to skip callbacks that are defined by objects, e.g. for
`ActionController`:

    skip_after_filter MySpecialFilter

Previously this didn't work due to a bug in how Rails compared callbacks
in `Callback#matches?`. When a callback is compiled, if it's an object
filter (i.e. not a method, proc, etc.), `Callback` now defines a method on
`@klass` that is derived from the class name rather than `@callback_id`.
So, when `skip_callback` tries to find the appropriate callback to
remove, `Callback` can regenerate the method name for the filter
object and return the correct value for `Callback#matches?`.
extract array to a constant
Merge pull request #10293 from vipulnsward/dont_mutate_callback

extract array to a constant
Merge pull request #10096 from benofsky/fix_skipping_object_callback_filters

Fixes skipping object callback filters
Move CHANGELOG entry to top

[ci skip]