Clean up prefix tests.
Use boost comparison test helpers, test one thing.
Coment cosmetic.
Fix stealth_info.ephem_pubkey (hash) misnomer.
Implement stealth_prefix input stream.
Add safe variants of from_big/little_endians.
Fix unsafe operation (guarded only by assert).
Merge pull request #126 from evoskuil/version2

Use comparative test helpers, test one thing, remove dead code.