support e=65537 for libmincrypt, DumpPublicKey

The output produced by DumpPublicKey now has a version tag on each
line (ie, each key).  The existing keys are retroactively dubbed
"version 1", and we add a version 2 for 2048-bit e=65537 keys.

Change-Id: I204ec615c8f2346670220a1aeb99269e4abd5f81