Fix load path for xbuilder/template
Fix infinite loop in Template#__new_instance

tap isn't defined on Xbuilder, since its a BlankSlate
Drop the escaping hack

libxml-ruby 2.3.4 includes the necessary fix (https://github.com/xml4r/libxml-ruby/commit/d381ef742a82d38de7afd64bfda83fa8cc2810f5).

Note that this changes the behaviour when creating a node with already-escaped text - xml.title('&amp') will now produce <title>&amp;amp;</title> instead of <title>&amp;</title>