dirs: back out forward-searching in finddirs() This backs out the changes below. The next patch will implement a faster algorithm based on backward-walking in finddirs(). 67241ee427cf (dirs._addpath: reinstate use of Py_CLEAR, 2015-04-07) 6f0e6fa9fdd7 (dirs._addpath: don't mutate Python strings after exposing them (issue4589), 2015-04-06) 1a9efc312700 (dirs.addpath: rework algorithm to search forward, 2015-03-27)