Support 4096-bit key generation on OpenPGP smartcards

Currently (GnuPG 1.x) the maximum size of keys that can be generated on a OpenPGP card is 3072 bits. Support for 4096 bit keys was added in GnuPG 2.0.18 and is not present in GnuPG 1.x.

Wheezy has GnuPG 2.0.19, so we should investigate installing both (see subticket).

Feature Branch: feature/6241-gnupg2

Subtasks

#7004 (closed)

Related issues

Blocked by #6015 (closed)

Original created by @sjmurdoch on 6241 (Redmine)

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