Inject 1.8/1.9 pure-ruby entry point during xcompile

The original problem of .so files not included in the final
gemspec is because rake-compiler put files in lib_dir/X.Y/extension
while the pure-ruby entry point was looking for lib_dir/XY/extension

tasks/compile.rake

@@ -21,6 +21,11 @@ Rake::ExtensionTask.new("mysql2", gemspec) do |ext|
     ext.cross_platform = ['x86-mingw32', 'x86-mswin32-60']
     ext.cross_config_options << "--with-mysql-include=#{mysql_lib}/include"
     ext.cross_config_options << "--with-mysql-lib=#{mysql_lib}/lib/opt"
+
+    # inject 1.8/1.9 pure-ruby entry point when cross compiling only
+    ext.cross_compiling do |spec|
+      spec.files << 'lib/mysql2/mysql2.rb'
+    end
   end
 
   ext.lib_dir = File.join 'lib', 'mysql2'
@@ -30,25 +35,16 @@ Rake::ExtensionTask.new("mysql2", gemspec) do |ext|
 end
 Rake::Task[:spec].prerequisites << :compile
 
-namespace :cross do
-  task :file_list do
-    gemspec.extensions = []
-    gemspec.files += Dir["lib/#{gemspec.name}/#{gemspec.name}.rb"]
-    gemspec.files += Dir["lib/#{gemspec.name}/1.{8,9}/#{gemspec.name}.so"]
-    # gemspec.files += Dir["ext/mysql2/*.dll"]
-  end
-end
-
-file 'lib/mysql2/mysql2.rb' do
+file 'lib/mysql2/mysql2.rb' do |t|
   name = gemspec.name
-  File.open("lib/#{name}/#{name}.rb", 'wb') do |f|
+  File.open(t.name, 'wb') do |f|
     f.write <<-eoruby
-require "#{name}/\#{RUBY_VERSION.sub(/\\.\\d+$/, '')}/#{name}"
+RUBY_VERSION =~ /(\\d+.\\d+)/
+require "#{name}/\#{$1}/#{name}"
     eoruby
   end
 end
 
 if Rake::Task.task_defined?(:cross)
   Rake::Task[:cross].prerequisites << "lib/mysql2/mysql2.rb"
-  Rake::Task[:cross].prerequisites << "cross:file_list"
 end