packet/packet.go: add ECDSA to the algorithms in CanSign() packet/signature.go: add support for the features subpacket (which is used to signal support for the MDC packet) openpgp/read_test.go: add a key generated by End-to-End as a testcase (End-to-End's keys are unusual: they set critical bits) Change-Id: Ifaf3922cd35ea27cf1276d7a8238dd50536eb4ed Reviewed-on: https://go-review.googlesource.com/2058 Reviewed-by: Adam Langley <agl@golang.org>