sort mrblib/*.rb files to compile (class.rb comes before error.rb); close #1132; close #1134

mrblib/mrblib.rake

@@ -6,7 +6,7 @@ MRuby.each_target do
   self.libmruby << objfile("#{current_build_dir}/mrblib")
 
   file objfile("#{current_build_dir}/mrblib") => "#{current_build_dir}/mrblib.c"
-  file "#{current_build_dir}/mrblib.c" => [mrbcfile] + Dir.glob("#{current_dir}/*.rb") do |t|
+  file "#{current_build_dir}/mrblib.c" => [mrbcfile] + Dir.glob("#{current_dir}/*.rb").sort do |t|
     mrbc_, *rbfiles = t.prerequisites
     FileUtils.mkdir_p File.dirname(t.name)
     open(t.name, 'w') do |f|