Made gpg-grep script executable.
Add hockeypuck load --verify-round-trip switch

Helps debug issues where the parsed key that Hockeypuck attempts to load
isn't the same when querying back out of the database. It's slow but
useful for debugging.
Correct handling of dup subkeys, fixes #9

Added check for duplicate subkeys in Resolve, dump them in unsupported
but keep for key hashing to maintain SKS compatibility.
Added testcase captured with 'load --verify-round-trip'.
Log warnings for key fetches that do not match their indexed digest.
Init signable to nil in OpaqueKeyring.Parse.