Fix test_index and test_rindex fail on ruby-2.x

String#index(i) and String#rindex(i) do not accept Numeric
as a parameter on ruby-2.0 or later.

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2544 f4f36d40-9719-0410-9868-dde021a23eda
Fix test_assign_nth_error fails on ruby-2.x

str[idx] = str allows idx == str.length on ruby-2.0 or later.

    # ruby-1.8
    str = "abc"
    str[2] = "d"
    p str
    => "abd"
    str[3] = "e"
    => IndexError

    # ruby-2.1
    str = "abc"
    str[2] = "d"
    p str
    => "abd"
    str[3] = "e"
    p str
    => "abde"
    str[5] = "f"
    => IndexError

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2545 f4f36d40-9719-0410-9868-dde021a23eda
Fix utility function with_kcode() to work on ruby-2.x

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2546 f4f36d40-9719-0410-9868-dde021a23eda
Fix test_ref_nth fails on ruby-2.x

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2547 f4f36d40-9719-0410-9868-dde021a23eda
Fix test_include fails on ruby-2.x

git-svn-id: https://svn.code.sf.net/p/rubycocoa/svn/trunk/src@2548 f4f36d40-9719-0410-9868-dde021a23eda