merge from ruby trunk
bumping version
remove unused variables
Merge pull request #186 from hsbt/backport-rubycore

remove unused variables
backport from ruby trunk
Merge branch 'backport-ruby-trunk'
added 2.1.0 for travis
	* ext/psych/lib/psych/visitors/yaml_tree.rb: support dumping Encoding
	  objects.

	* ext/psych/lib/psych/visitors/to_ruby.rb: support loading Encoding
	  objects.

	* test/psych/test_encoding.rb: add test

	* ext/psych/lib/psych.rb: add version
backport from libyaml-1.1.6
Merge pull request #187 from tenderlove/libyaml-0.1.6

backport from libyaml-1.1.6
bumping up version
0x80 to 0x9F should be dumped by libyaml differently.

They should be dumped as "\u0080", not "\x80". For example, U+0092
needs to be represented as "\u0092" ("\xC2\x92"), not simply "\x92".
These two have completely different meanings.

Realistically, this should be a pullrequest to libyaml, but I am lazy.