Bugs found

Bugs found before using the Small Eigen Collider, causing me to create it

https://github.com/rubinius/rubinius/issues/513 - StringIO#gets doesn't handle multiple characters for sep_string
https://github.com/rubinius/rubinius/issues/505 - String#split gives an incorrect output when a leading delimiter is included

https://github.com/rubinius/rubinius/issues/1005 - String#partition not consistent with MRI when passed a block and argument
https://github.com/rubinius/rubinius/issues/694 - YAML.try_implicit can cause a segfault
https://github.com/rubinius/rubinius/issues/659 - Set_superclass can be used to trigger a segfault
https://github.com/rubinius/rubinius/issues/643 - Segfaults can be triggered using ObjectSpace.undefine_finalizer(:symbol)
https://github.com/rubinius/rubinius/issues/518 - String#casecmp gives the opposite result to what it should

http://redmine.ruby-lang.org/issues/show/4367 - Thread.kill segfaults when the object to be killed isn't a thread
http://redmine.ruby-lang.org/issues/show/4342 - YAML raises an exception while parsing certain regular expressions
http://redmine.ruby-lang.org/issues/show/4059 - String#unpack can segfault when passed a block