PGPUID objects should be comparable when no selfsig exists.
PGPUID objects should be comparable when no selfsig exists.

In some cases, no selfsig will exist for PGPUID.  In the event that a
selfsig-less PGPUIDs is compared with one that has a selfsig, the
missing selfsig should be "less than" the other.

Signed-off-by: Daniel Kahn Gillmor <b1356865a0eefd1fb76a8b663fad027be4bc9b61@fifthhorseman.net>

SecurityInnovation/PGPy,SecurityInnovation/PGPy,SecurityInnovation/PGPy