Allow multiple preserve_exact_body_bytes hooks.

This will pave the way to make it easy to support a cassette option for this feature.

lib/vcr/configuration.rb

@@ -393,16 +393,14 @@ def configure_rspec_metadata!
     #  with a non-standard encoding or with a body containing invalid bytes for the given
     #  encoding. Note that when you set this, and the block returns true, you sacrifice
     #  the human readability of the data in the cassette.
-    def preserve_exact_body_bytes(&block)
-      @preserve_exact_body_bytes_block = block
-    end
+    define_hook :preserve_exact_body_bytes
 
     # @return [Boolean] whether or not the body of the given HTTP message should
     #  be base64 encoded during serialization in order to preserve the bytes exactly.
     # @param http_message [#body, #headers] the `VCR::Request` or `VCR::Response` object being serialized
     # @see #preserve_exact_body_bytes
     def preserve_exact_body_bytes_for?(http_message)
-      @preserve_exact_body_bytes_block.call(http_message, VCR.current_cassette)
+      invoke_hook(:preserve_exact_body_bytes, http_message, VCR.current_cassette).any?
     end
 
   private

spec/vcr/cassette_spec.rb

@@ -421,6 +421,8 @@ def stub_old_interactions(interactions)
       cassette = VCR::Cassette.new('example', :tag => :foo)
       cassette.stub!(:new_recorded_interactions).and_return(interactions)
 
+      VCR.configuration.stub(:invoke_hook).and_return([false])
+
       interactions.each do |i|
         VCR.configuration.should_receive(:invoke_hook).with(
           :before_record,

spec/vcr/configuration_spec.rb

@@ -222,6 +222,14 @@ def message_for(body)
       subject.preserve_exact_body_bytes_for?(message_for "b").should be_false
     end
 
+    it "returns true when any of the registered blocks returns true" do
+      called_hooks = []
+      subject.preserve_exact_body_bytes { called_hooks << :hook_1; false }
+      subject.preserve_exact_body_bytes { called_hooks << :hook_2; true }
+      subject.preserve_exact_body_bytes_for?(message_for "a").should be_true
+      called_hooks.should eq([:hook_1, :hook_2])
+    end
+
     it "invokes the configured hook with the http message and the current cassette" do
       cassette = stub(:cassette)
       VCR.should respond_to(:current_cassette)