Decode gzip'd responses like Ruby 1.9

Thanks to carsonmcdonald for the inspiration
Closes gh-40

features/handles_compressed_responses.feature

@@ -10,3 +10,10 @@ Feature: Handles Compressed Responses
     And that service is accessed at the path '/service.html'
     When I call HTTParty#get with '/service.html'
     Then the return value should match '<h1>Some HTML</h1>'
+
+  Scenario: Supports gzip encoding
+    Given a remote gzip service
+    And the response from the service has a body of '<h1>Some HTML</h1>'
+    And that service is accessed at the path '/service.html'
+    When I call HTTParty#get with '/service.html'
+    Then the return value should match '<h1>Some HTML</h1>'

features/steps/mongrel_helper.rb

@@ -31,6 +31,26 @@ class DeflateHandler < BasicMongrelHandler
   end
 end
 
+class GzipHandler < BasicMongrelHandler
+  def process(request, response)
+    response.start do |head, body|
+      head['Content-Encoding'] = 'gzip'
+      body.write gzip(response_body)
+    end
+  end
+
+  protected
+
+  def gzip(string)
+    sio = StringIO.new('', 'r+')
+    gz = Zlib::GzipWriter.new sio
+    gz.write string
+    gz.finish
+    sio.rewind
+    sio.read
+  end
+end
+
 module BasicAuthentication
   def self.extended(base)
     base.custom_headers["WWW-Authenticate"] = 'Basic Realm="Super Secret Page"'

features/steps/remote_service_steps.rb

@@ -21,6 +21,10 @@ Given /^a remote deflate service$/ do
   @handler = DeflateHandler.new
 end
 
+Given /^a remote gzip service$/ do
+  @handler = GzipHandler.new
+end
+
 Given /the response from the service has a Content-Type of '(.*)'/ do |content_type|
   @handler.content_type = content_type
 end