Inner Method errors are handled as related to outer Method call

### Was: current_actor, proc, and exceptions

i am writing dsl and evaling outer procs (and pass current_actor into proc).
when any exception happens in the proc, i dont what my actor to die.

example:
```ruby
require 'bundler/setup'
require 'celluloid'

class A
  include Celluloid

  def initialize(outer_proc)
    @proc = outer_proc
  end

  def exec
    @proc.call current_actor
  rescue => ex
    p ex
  end

end

x = eval "->(a) { p a; a.wtf? }"
a = A.new(x)
a.exec

p a.alive?
```
false

if i pass `self` instead of `current_actor` returns true (but wiki says self is bad when calling code outside the actor, proc can be evaled in another actor). 
In 0.13 also this code returns true.