Fix YAML deserialization of anonymous structs

`DelayedJob` makes freedom patches of `Psych`'s `resolve_class` method.
It misses to guard this method from empty class names.

`Psych` does it:
https://github.com/tenderlove/psych/blob/2c644e18/lib/psych/class_loader.rb#L25

While deserializing an anonymous struct the class name is an empty
string (`""`). Constantizing an empty string resolves to `Object`.

This leads to this error:

    #<NoMethodError: undefined method `members' for #<Object:0xXXXXXXX>>

After this commit deserializing anonymous structs works again.
Add custom Psych Visitor's behavior only for Delayed, not glabally
Fix support for ruby 1.9.2 (Psych < 1.3.0)
Add support to Ruby 2.1
Override even fewer YAML methods
Don't override AR yaml generation
Use a throw away log file
Merge branch 'pr/612' into separate-yaml

Conflicts:
	lib/delayed/psych_ext.rb
Load psych in rubinius

It doesn't do this on its own
Merge pull request #710 from collectiveidea/separate-yaml

Separate yaml