Use "make install" instead of manually copying extension binary (#191)

Until now rake-compiler uses "make" to build the extension binary, but doesn't use "make install" to copy it into the lib directory.
This has the downside, that only the extension binary is copied, but no additional files.
In particular files registered per mkmf's $INSTALLFILES mechanism are not respected.
Using "make install" fixes this.

lib/rake/extensiontask.rb

@@ -115,6 +115,7 @@ def define_compile_tasks(for_platform = nil, ruby_ver = RUBY_VERSION)
       tmp_path = "#{@tmp_dir}/#{platf}/#{@name}/#{ruby_ver}"
       stage_path = "#{@tmp_dir}/#{platf}/stage"
 
+      siteconf_path = "#{tmp_path}/.rake-compiler-siteconf.rb"
       tmp_binary_path = "#{tmp_path}/#{binary_path}"
       tmp_binary_dir_path = File.dirname(tmp_binary_path)
       stage_binary_path = "#{stage_path}/#{lib_path}/#{binary_path}"
@@ -132,10 +133,27 @@ def define_compile_tasks(for_platform = nil, ruby_ver = RUBY_VERSION)
       directory lib_binary_dir_path
       directory stage_binary_dir_path
 
+      directory File.dirname(siteconf_path)
+      # Set paths for "make install" destinations
+      file siteconf_path => File.dirname(siteconf_path) do
+        File.open(siteconf_path, "w") do |siteconf|
+          siteconf.puts "require 'rbconfig'"
+          siteconf.puts "require 'mkmf'"
+          siteconf.puts "dest_path = mkintpath(#{File.expand_path(lib_path).dump})"
+          %w[sitearchdir sitelibdir].each do |dir|
+            siteconf.puts "RbConfig::MAKEFILE_CONFIG['#{dir}'] = dest_path"
+            siteconf.puts "RbConfig::CONFIG['#{dir}'] = dest_path"
+          end
+        end
+      end
+
       # copy binary from temporary location to final lib
       # tmp/extension_name/extension_name.{so,bundle} => lib/
-      task "copy:#{@name}:#{platf}:#{ruby_ver}" => [lib_binary_dir_path, tmp_binary_path] do
-        install tmp_binary_path, "#{lib_path}/#{binary_path}"
+      task "copy:#{@name}:#{platf}:#{ruby_ver}" => [lib_binary_dir_path, tmp_binary_path, "#{tmp_path}/Makefile"] do
+        # install in lib for native platform only
+        unless for_platform
+          sh "#{make} install", chdir: tmp_path
+        end
       end
       # copy binary from temporary location to staging directory
       task "copy:#{@name}:#{platf}:#{ruby_ver}" => [stage_binary_dir_path, tmp_binary_path] do
@@ -164,12 +182,12 @@ def define_compile_tasks(for_platform = nil, ruby_ver = RUBY_VERSION)
 
       # makefile depends of tmp_dir and config_script
       # tmp/extension_name/Makefile
-      file "#{tmp_path}/Makefile" => [tmp_path, extconf] do |t|
+      file "#{tmp_path}/Makefile" => [tmp_path, extconf, siteconf_path] do |t|
         options = @config_options.dup
 
         # include current directory
         include_dirs = ['.'].concat(@config_includes).uniq.join(File::PATH_SEPARATOR)
-        cmd = [Gem.ruby, "-I#{include_dirs}"]
+        cmd = [Gem.ruby, "-I#{include_dirs}", "-r#{File.basename(siteconf_path)}"]
 
         # build a relative path to extconf script
         abs_tmp_path = (Pathname.new(Dir.pwd) + tmp_path).realpath