use Capybara.server_port if specified

lib/capybara.rb

@@ -14,6 +14,7 @@ module Capybara
 
   class << self
     attr_accessor :asset_root, :app_host, :run_server, :default_host
+    attr_accessor :server_port
     attr_accessor :default_selector, :default_wait_time, :ignore_hidden_elements
     attr_accessor :save_and_open_page_path
 

lib/capybara/server.rb

@@ -73,7 +73,7 @@ module Capybara
         @port = Capybara::Server.ports[@app.object_id]
           
         if not @port or not responsive?
-          @port = find_available_port
+          @port = Capybara.server_port || find_available_port
           Capybara::Server.ports[@app.object_id] = @port
 
           Thread.new { handler.run(Identify.new(@app), :Port => @port, :AccessLog => []) }

spec/server_spec.rb

@@ -17,6 +17,18 @@ describe Capybara::Server do
     end.should_not raise_error
   end
   
+  it "should use specified port" do
+    Capybara.server_port = 22789
+
+    @app = proc { |env| [200, {}, "Hello Server!"]}
+    @server = Capybara::Server.new(@app).boot
+    
+    @res = Net::HTTP.start(@server.host, 22789) { |http| http.get('/') }
+    @res.body.should include('Hello Server')
+
+    Capybara.server_port = nil
+  end
+  
   it "should find an available port" do
     @app1 = proc { |env| [200, {}, "Hello Server!"]}
     @app2 = proc { |env| [200, {}, "Hello Second Server!"]}