Escape multibyte line terminators in JSON encoding

Currently, json/encoding respects the JSON spec (as it should) which 
disallows \n and \r inside strings, escaping them as expected.

Unfortunately, ECMA-262 (Javascript) disallows not only \n and \r in 
strings, but "Line Terminators" which includes U+2028 and U+2029. 
See here: http://bclary.com/2004/11/07/#a-7.3

This pull request adds U+2028 and U+2029 to be escaped.

# Why? 

It's very common to see something like this in a Rails template:

<script type="text/javascript"> 
var posts = <%= @posts.to_json %>;
</script>

If U+2028 or U+2029 are part of any attributes output in the to_json
call, you will end up with an exception.
In Chrome: Uncaught SyntaxError: Unexpected token ILLEGAL 

# Why not?

This is JSON encoding, and the JSON spec is specific about how to 
encode strings. U+2028 and U+2029 don't get special treatment.

Just trying to start a discussion... what do you do in your apps
to deal with this? Is there a convention I'm missing?
Remove current_adapter? from test_sanitize_sql_hash_handles_associations

Because of each adapter implementation differences,
`expected_value` string needed to be handled by each adapter.
This commit removes current_adapter
by using ActiveRecord::ConnectionAdapters::Quoting methods.
dependency ActiveSupport::Deprecation
Merge pull request #10519 from eiel/dependency-core_ext-hash-diff

dependency ActiveSupport::Deprecation
Use ruby's Encoding support for tidy_bytes

The previous implementation was quite slow. This leverages some of the
transcoding abilities built into Ruby 1.9 instead. It is roughly 96%
faster.

The roundtrip through UTF_8_MAC here is because ruby won't let you
transcode from UTF_8 to UTF_8. I chose the closest encoding I could
find as an intermediate.
adding test to demonstrate inconsistencies in the AS::Callbacks api
refactor tests for more points
adding more tests around callback inconsistencies
Merge pull request #10521 from yahonda/sanitize_oracle

Remove current_adapter? from test_sanitize_sql_hash_handles_associations
Using define method instead of class eval when defining model callbacks.
Based on my benchmark results, this change improves performance
substantially when defining callbacks.

This benchmark (https://gist.github.com/wangjohn/5542610) was run using
the current master and also using my experimental branch which replaced
class_eval with define_single_method.

Using class_eval (current master):

                    user     system      total        real
10 trials       0.000000   0.000000   0.000000 (  0.001568)
50 trials       0.020000   0.000000   0.020000 (  0.021715)
500 trials      0.110000   0.000000   0.110000 (  0.115357)
1000 trials     0.250000   0.000000   0.250000 (  0.260025)
10000 trials    2.560000   0.000000   2.560000 (  2.568408)
50000 trials   12.800000   0.010000  12.810000 ( 12.886871)

Using define_single_method (experimental branch):

                    user     system      total        real
10 trials       0.000000   0.000000   0.000000 (  0.000790)
50 trials       0.000000   0.000000   0.000000 (  0.002960)
500 trials      0.050000   0.010000   0.060000 (  0.055690)
1000 trials     0.100000   0.000000   0.100000 (  0.094073)
10000 trials    0.890000   0.000000   0.890000 (  0.900364)
50000 trials    4.650000   0.000000   4.650000 (  4.686127)
Merge pull request #10355 from burke/master

Use Ruby's native Encoding functionality to implement `tidy_bytes`
we need to indicate the type of callback
polymorphic comparison operator
fix object comparison case
if the callbacks are not the same class, they cannot be duplicates
separate filters from source code
Merge pull request #10524 from wangjohn/define_method_for_callbacks

Using define method instead of class eval when defining model callbacks.
extracted piece of code into a method

In order to fix #10421 I need to enable merge to take an option
so that relations could be merged without making the last where
condition to win.

That fix would forever reside in 4-0-stable branch and would not be
merged to master since using scope without lambda has been deprecated.

In this commit I have extracted code into a method and I think it
makes code look better. Hence the request to merge it in both
master and 4-0-stable.

If there is any concern then this code can be merged only in
4-0-stable and that would be fine too.
separate identification computation
Merge branch 'polycb'

* polycb:
  separate identification computation
  separate filters from source code
  if the callbacks are not the same class, they cannot be duplicates
  fix object comparison case
  polymorphic comparison operator