[Feature #13884]

Reduce number of memory allocations for "and", "or" and "diff"
operations on small arrays

Very often, arrays are used to filter parameters and to select
interesting items from 2 collections and very often these
collections are small enough, for example:

```ruby
SAFE_COLUMNS = [:id, :title, :created_at]

def columns
  @all_columns & SAFE_COLUMNS
end
```

In this patch, I got rid of unnecessary memory allocations for
small arrays when "and", "or" and "diff" operations are performed.

name             | HEAD  | PATCH
-----------------+------:+------:
array_small_and  | 0.615 | 0.263
array_small_diff | 0.676 | 0.282
array_small_or   | 0.953 | 0.463

name             | PATCH
-----------------+------:
array_small_and  | 2.343
array_small_diff | 2.392
array_small_or   | 2.056

name             | HEAD  | PATCH
-----------------+------:+------:
array_small_and  | 1.429 | 1.005
array_small_diff | 1.493 | 0.878
array_small_or   | 1.672 | 1.152

name             | PATCH
-----------------+------:
array_small_and  | 1.422
array_small_diff | 1.700
array_small_or   | 1.452

Author:    Dmitry Bochkarev <dimabochkarev@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60057 b2dd03c8-39d4-4d8f-98ff-823fe69b080e