Context::Preserve(3pm) on Linux

The text c3df0a5f8c1d, as Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze) shipped it.

run code after a subroutine call, preserving the context the subroutine would have seen if it were the last statement in the caller