Make error handling work on older versions of libxml_ruby.  Fixes
Make error handling work on older versions of libxml_ruby.  Fixes

sferik/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,increments/libxml-ruby,sferik/libxml-ruby,sferik/libxml-ruby,xml4r/libxml-ruby,xml4r/libxml-ruby,increments/libxml-ruby,sferik/libxml-ruby,increments/libxml-ruby