Use full fingerprints for key comparisons for keys fetched by URI

When installing a key from a local file or over http, do a full
fingerprint comparison, don't just compare the last 4 bytes.
[COOK-3052] Handle long key-IDS correctly

Match key IDs against the end of the fingerprints in the keyring.
[COOK-1856] Case-insensitively compare key-IDs
Merge pull request #49 from yola/repository-fingerprints

Long GPG key-IDs