Update textproc/ruby-xmlparser to 0.7.1.

* Use lang/ruby/gem.mk instead of misc/rubygems/rubygem.mk.
* Add PKG_DESTDIR_SUPPORT.
* Ajust new ruby package's framework.

Changes of version 0.7.1

    * convert the encoding of an input string automatically (Ruby 1.9.1).

Changes of version 0.7.0

    * suppot Ruby 1.9.1.
    * remove some experimental libraries.
    * remove all example programs.

(taca)