git-svn: write memoized data explicitly to avoid Storable bug

git-svn: write memoized data explicitly to avoid Storable bug

Apparently using the Storable module during global destruction is
unsafe - there is a bug which can cause segmentation faults:

  http://rt.cpan.org/Public/Bug/Display.html?id=36087
  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=482355

The persistent memoization support introduced in commit 8bff7c538
relied on global destruction to write cached data, which was leading
to segfaults in some Perl configurations.  Calling Memoize::unmemoize
in the END block forces the cache writeout to be performed earlier,
thus avoiding the bug.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Acked-by: Eric Wong <normalperson@yhbt.net>