Core: ngx_conf_set_access_slot() user access (ticket #1096).
Core: ngx_conf_set_access_slot() user access (ticket #1096).

Previously, user access bits were always set to "rw" unconditionally,
even with "user:r" explicitly specified.  With this change we only add
default user access bits (0600) if they weren't set explicitly.

hy0kl/nginx,hy0kl/nginx,hy0kl/nginx