portation of spec tests

Today, I port all the spec tests about yaml from rubinius to rbyaml.
In order to make all of them could be passed smoothly by rbyaml library, I fixed three small bugs.

1. As RbYAML.tagged_classes, Given int tag uri, Should return Integer .
RbYAML.tagged_classes["tag:yaml.org,2002:int"].should == Integer
2. As Symbol.to_yaml, Should return symbol YAML representation.
:symbol.to_yaml.should ==  "--- :symbol\n"
3. As RbYAML, Should have tagurize method.
RbYAML.tagurize('wtf').should == "tag:yaml.org,2002:wtf"
RbYAML.tagurize(1).should == 1

Rubinius and Syck really help me a lot during improving rbyaml.
Thank them.