Add specific option for auto-key-retrieve

* src/common_inde.p (opt): Add it.
* src/main.c (read_options): Read it.
* src/parsecontroller.common_inde (ParseController::parse): Use it.

This is a new default off option. With the delays coming
from many SKS-Keyservers we can't use it in good consicence
yet it is just too slow if communicating with people that
have not published their keys.