Add a simple Proc extension to support bindings (#1240)

This removes the dependency on the contextual_proc gem

Fixes: #1238

spec/support/binding_proc.rb

@@ -0,0 +1,24 @@
+##
+# A simple extension of the Proc class that supports setting a custom binding
+# and evaluates everything in the Proc using the new binding.
+
+class ProcWithBinding < Proc
+  ##
+  # Set the binding for this instance
+
+  def apply_binding(bind, *args)
+    @binding = bind
+    instance_exec(*args, &self)
+  end
+
+  def method_missing(method, *args)
+    begin
+      method_from_binding = eval("method(#{method.inspect})", @binding)
+      return method_from_binding.call(*args)
+    rescue NameError
+      # fall through on purpose
+    end
+
+    super
+  end
+end