agent: New option --auto-expand-secmem.
* agent/gpg-agent.c (oAutoExpandSecmem): New enum value. (opts): New option --auto-expand-secmem. (main): Implement that option.
Note that this option has an effect only if Libgcrypt >= 1.8.2 is
used.
- GnuPG-bug-id: T3530