ShowDocSpec: add a test concerning monkeypatching

Make sure that `show-doc` displays the comments of the original
definition by default. This test *must* fail with current state of
things. The goal is to eliminate the oddities in Pry across some Ruby
implementations.

For more information see:
d05233ecd3

spec/commands/show_doc_spec.rb

@@ -263,7 +263,18 @@ if !PryTestHelpers.mri18_and_no_real_source_location?
         end
 
         describe "messages relating to -a" do
-          it 'indicates all available monkeypatches can be shown with -a when' \
+          it "displays the original definition by default (not a doc of a monkeypatch)" do
+            class TestClassForCandidatesOrder
+              def beta
+              end
+            end
+
+            result = pry_eval("show-doc TestClassForCandidatesOrder")
+            result.should =~ /Number of monkeypatches: 2/
+            result.should =~ /The first definition/
+          end
+
+          it 'indicates all available monkeypatches can be shown with -a ' \
             '(when -a not used and more than one candidate exists for class)' do
             # Still reading boring tests, eh?
             class TestClassForShowSource

spec/fixtures/show_source_doc_examples.rb

@@ -1,4 +1,4 @@
-# used by test_show_source.rb and test_documentation.rb
+# used by show_source_spec.rb and show_doc_spec.rb
 class TestClassForShowSource
   #doc
   def alpha
@@ -14,3 +14,9 @@ class TestClassForShowSourceInstanceEval
   def alpha
   end
 end
+
+# The first definition (find the second one in show_doc_spec.rb).
+class TestClassForCandidatesOrder
+  def alpha
+  end
+end