Support for 'python2' executable

This fix is needed to make the gem compile on Arch Linux.

ext/libv8/builder.rb

@@ -26,6 +26,22 @@ def make_flags(*flags)
 
     def build_libv8!
       Dir.chdir(File.expand_path '../../../vendor/v8', __FILE__) do
+        # Replace all mentions of "python" with "python2" if the executable
+        # is in the path. This is an issue for Arch Linux, which is also
+        # where the following fix comes from.
+        # See: https://projects.archlinux.org/svntogit/community.git/tree/trunk/PKGBUILD?h=packages/v8
+        if system('which python2') &&
+           !File.open('Makefile', 'r').read.include?('python2')
+          system <<-'EOF'
+            find build/ test/ tools/ src/ -type f \
+              -exec sed -e 's_^#!/usr/bin/env python$_&2_' \
+                        -e 's_^\(#!/usr/bin/python2\).[45]$_\1_' \
+                        -e 's_^#!/usr/bin/python$_&2_' \
+                        -e "s_'python'_'python2'_" -i {} \;
+          EOF
+          system "sed -i 's/python /python2 /' Makefile"
+        end 
+
         puts `env CXX=#{compiler} LINK=#{compiler} #{make} #{make_flags}`
       end
       return $?.exitstatus