Make Rubinius.add_defn_method return the name of the def'd method, as a symbol

This makes the Rubinius behavior compatible with MRI 2.1,
which now sports a specified return value for def.

>> (def foo; end) #=> :foo

See RubySpec:
  https://github.com/rubyspec/rubyspec/commit/e567d2458e46c12e50c85394f509f3b5a5688e11
Update test fixtures that relied on CompiledCode returned from def.

Some of the spec/core test fixtures were relying on the CompiledCode
instance getting returned from a method definition.

These fixtures were updated to fetch the CompiledCode instance from
the symbol, using instance_method to get the UnboundMethod instance,
which in turn holds the CompiledCode instance as its executable.

>> def foo; end #=> :foo
>> instance_method(:foo).executable #=> #<Rubinius::CompiledCode ...>
Add specs to ensure all Enumerable classes include Enumerable
Add specs to ensure all Comparable classes include Comparable
Include Comparable module in Symbol class
Merge pull request #2870 from sferik/comparable_symbol

Make Symbol Comparable
Fixed JIT API broken by 5565ed88.
Merge pull request #2868 from jemc/def_return_symbol

Method def should return Symbol instead of CompiledCode
Revert "Merge pull request #2868 from jemc/def_return_symbol"

We only want to change the API exposing the behavior that MRI changed. We
don't want to change our own API.

Also need to rewrite these specs. Many spec descriptions are insufficient (eg
"has the correct value" is not an acceptable spec).

See later commits for the fixes.

This reverts commit 180466bf51b0a79ef2888e2797aaac85f9ac6714, reversing
changes made to 7c6c45276806d3b66c179193668fda491b6ddba8.
Updated CI specs to RubySpec 57e46a24.
Removed problematic spec.

We need a better mechanism for obtaining the comparison value.
Return the method name from def.
Updated inline cache specs.
Fixed some CompiledCode specs.
Moved benchmark/ to rubinius-benchmark repository.
Removed obsolete library/bin/rar.rb.
Fixed shebang in library/bin/irb.rb.
Fixed pre-installing gems to update bin wrapper shebang.
Remove executable permission from source files
Merge pull request #2883 from henrikhodne/hh-remove-exec-perm-vendor-udis86

Remove executable permission from source files