Suppress waring "unused variable"

- suppress warning unused variable in rubycocoa_app_init().
- delete unused variable in strenc_rb2oc().

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2623 f4f36d40-9719-0410-9868-dde021a23eda
Allow Ruby-2.0 or later

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2624 f4f36d40-9719-0410-9868-dde021a23eda