We've found we need a way to cause a change in signatures and move
to a new hash 'namespace' with hashequiv. This introduces a variable
which allows us to do this.
(From OE-Core rev: 1c2d5aeae2fa2dfc16bc60b6cf0b310f826337fd)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>