Move `Kernel.local_variables` to core.
Add 'Raise in rescue' test to exception.
Merge pull request #2296 from take-cheeze/core_local_vars

Move `Kernel.local_variables` to core.
Merge branch 'add-exception-test' of https://github.com/yui-knk/mruby into yui-knk-add-exception-test
correct comment; ref #2297
update raise in ensure test
Merge branch 'master' of github.com:mruby/mruby