Update to use a new shared_example style

This refactors all the shared example sets to use the newer
`shared_example` style definitions. To use these example sets do, e.g.:

   it_behaves_like 'an RDF::Enumerable'

This also shifts from the pattern of defining `@instance_variables` in a
`before` block to using `let` (We might consider using shared example
arguments instead).

Author: Tom Johnson

lib/rdf/spec/countable.rb

@@ -1,27 +1,28 @@
 require 'rdf/spec'
 
-module RDF_Countable
-  extend RSpec::SharedContext
+RSpec.shared_examples 'an RDF::Countable' do
   include RDF::Spec::Matchers
 
-  before :each do
-    raise '+@countable+ must be defined in a before(:each) block' unless instance_variable_get('@countable')
+  before do
+    raise 'countable must be set with `let(:countable)' unless
+      defined? countable
 
     @statements = RDF::Spec.quads
 
-    if @countable.empty?
-      if (@countable.writable? rescue false)
-        @countable.insert_statements(@statements)
-      elsif @countable.respond_to?(:<<)
-        @statements.each { |statement| @countable << statement }
+    if countable.empty?
+      if (countable.writable? rescue false)
+        countable.send(:insert_statements, @statements)
+      elsif countable.respond_to?(:<<)
+        @statements.each { |statement| countable << statement }
       else
-        raise "+@countable+ must respond to #<< or be pre-populated with the statements in #{RDF::Spec::TRIPLES_FILE} in a before(:each) block"
+        raise "+countable+ must respond to #<< or be pre-populated with the" \
+              "statements in #{RDF::Spec::TRIPLES_FILE} in a before block"
       end
     end
   end
 
   describe RDF::Countable do
-    subject {@countable}
+    subject {countable}
 
     it {should respond_to(:empty?)}
     it {should_not be_empty}

lib/rdf/spec/durable.rb

@@ -14,15 +14,15 @@
 #      File.delete('test.db') if File.exists?('test.db')
 #    end
 #
-#    include RDF_Repository
+#    it_behaves_like 'an RDF::Repository'
 #  end
 #end
-module RDF_Durable
-  extend RSpec::SharedContext
+RSpec.shared_examples 'an RDF::Durable' do
   include RDF::Spec::Matchers
 
   before :each do
-    raise '+@load_durable+ must be defined in a before(:each) block' unless instance_variable_get('@load_durable')
+    raise '+@load_durable+ must be defined in a before(:each) block' unless
+      instance_variable_get('@load_durable')
   end
 
   describe RDF::Durable do