fs.rmtree: do not make symlinks writable before removing them
fs.rmtree: do not make symlinks writable before removing them

REASON: chmod is passed through links, which is unintended and can fail

Fixes "bead nuke fails on virtualenv directories" #28

e3krisztian/bead,krisztianfekete/lib,e3krisztian/bead,krisztianfekete/lib