Add check that proof has been populated in the errinfo spec.

(cherry picked from commit 6e58fa8)

Author: aardvark179

spec/ruby/optional/capi/kernel_spec.rb

@@ -313,9 +313,11 @@
       @s.rb_protect_null_status(42) { |x| raise }.should == nil
     end
 
-    it "ppoulates errinfo with the captured exception" do
+    it "poulates errinfo with the captured exception" do
       proof = []
       @s.rb_protect_errinfo(77, proof) { |x| raise NameError }.class.should == NameError
+      proof[0].should == 23
+      proof[1].should == nil
     end
 
   end