mail/ruby-rfilter: fix build with Ruby 2.2

mail/ruby-rfilter/files/patch-install.rb

@@ -0,0 +1,20 @@
+--- install.rb.orig	2016-04-04 21:38:57 UTC
++++ install.rb
+@@ -45,7 +45,7 @@ end
+ 
+ class ConfigTable
+ 
+-  c = ::Config::CONFIG
++  c = ::RbConfig::CONFIG
+ 
+   rubypath = c['bindir'] + '/' + c['ruby_install_name']
+ 
+@@ -692,7 +692,7 @@ class Installer
+         "no extention exists: Have you done 'ruby #{$0} setup' ?"
+   end
+ 
+-  DLEXT = /\.#{ ::Config::CONFIG['DLEXT'] }\z/
++  DLEXT = /\.#{ ::RbConfig::CONFIG['DLEXT'] }\z/
+ 
+   def _allext( dir )
+     Dir.open(dir) {|d|