Fix RubySass compile error for non-ascii characters

If a sass file contains non-ascii characters, sass compiling fails
with invalid multibyte char (US-ASCII) error on Windows 7 with
JRuby 1.7.x.

JRuby 1.7.x works with Ruby 1.9 mode by default.
We convert string to Unicode code point representaion to fix
compile error.

We set org.jruby.embed.compat.version 1.9 for JRuby 1.6.x.