Update p5-Scope-Upper to 0.18.

Changes from previous:
0.18    2011-10-10 20:50 UTC
        + Add : The uid() function returns an unique identifier for each dynamic
                scope. The validate_uid() function can be used to check whether
                one such identifier is valid (i.e. that the scope it refers to
                is still alive).
        + Chg : It is no longer possible on perl 5.6 to call goto() in an
                uplevel callback to replace the uplevel call. This change was
                needed in order to ensure consistency between platforms
                regarding to the following fix just below.
        + Fix : The uplevel() tests now pass on Windows.
                Thanks C.H. Kang for bringing this to my attention.

0.17    2011-10-03 21:45 UTC
        + Fix : uplevel() will now use the correct pad when executing its
                callback. This fixes at least two issues :
                - closures defined inside the uplevel callback can now correctly
                access lexicals from inside and outside the callback.
                - state variables in the uplevel callback now work properly.
        + Fix : It is now generally possible to call goto() in the uplevel'd
                code to replace the uplevel stack frame. There are two cases
                for which it is still not possible :
                - if -D flags were set when running perl (as in "perl -Dt ...").
                - if the perl runloop has been replaced with a custom one by
                another module.
                If uplevel() detects that the replacement code contains a goto
                statement, and is in one of those two cases, then it will refuse
                to execute the callback and throw an exception.
                Note that this fix implies a run-time overhead of uplevel()
                proportional to the size of the the callback in every case
                (with a small ratio), and proportional to the size of ALL the
                code executed as the result of the uplevel call (including
                subroutine calls inside the callback) when a goto statement is
                found in the uplevel callback.
        + Fix : uplevel() has been taught how to handle XS callbacks properly.
        + Fix : The cause of "Attempt to free unreferenced scalar" warnings
                when using uplevel() has been addressed.
        + Fix : [RT #71212] : build failure on Windows.
                The module does no longer rely on calling Perl_cv_clone, which
                isn't exported.
                Thanks C.H. Kang for reporting.

(hiramatsu)