version up : nginx 1.7.5.

also use the explicit version of nginx-dav-ext-module.
also remove too old nginx-unstable.
update : bash 4.3 patchlevel 25, including fix for CVE-2014-6271.
Correct md5sum
erp5: Freeze ERP5
ERP5: pin revision
ERP5: use slapos.recipe.build 0.12
Revert "ERP5: use slapos.recipe.build 0.12"

This reverts commit 1acc85716ee09f89a3850e69396a6aa87831a58f.
ERP5: pin revision