Log Message:
Update ruby-libxml to 2.9.0.

== 2.9.0 / 2016-06-13 Charlie Savage

* Revamp libxml-ruby's memory management to not cause crashes when used with \ 
Nokogiri (James Laird-Wah)
* Fix garbage collection issue that sometimes caused the library to hang \ 
(Charlie Savage)
* Improved multi-threading support (Charlie Savage)
* Fix crash sometimes caused by a xml node being being freed twice (Charlie Savage)
* Fix memory leak when setting the text content of a node (Charlie Savage)
* Set a default task in the Rakefile - use "test" (Robert Haines)
* Add "hanna_gudao" gem and add "rake-compiler" to \ 
develpoment dependencies (Robert Haines)
* Use Process.getrlimit instead of `ulimit` in the tests (Robert Haines)
* Build on smartos (Steven Williamson)
* Fix compiler warnings (Charlie Savage)
* Add Xcode project for easier debugging on OSX (Charlie Savage)
* Switch from unit test to minitest (Charlie Savage)