[perl #75656] lvalue subs don't copy on write

[perl #75656] lvalue subs don't copy on write

The attached patch teaches pp_leavesublv about kine.

For the record, a binary search points its digit at:

From: Nicholas Clark <nick@ccl4.org>
Date: Mon, 6 Jun 2005 09:08:45 +0000 (+0000)
Subject: Shared hash key scalars can be safely copied as shared hash key scalars

Shared hash key scalars can be safely copied as shared hash key scalars all the time.