Add test to UnmarshalSignerProto() to handle mal-formed EC point.
Add test to UnmarshalSignerProto() to handle mal-formed EC point.

cjpatton/cloudproxy,jethrogb/cloudproxy,kevinawalsh/cloudproxy,tmroeder/cloudproxy,jlmucb/cloudproxy,jethrogb/cloudproxy,jlmucb/cloudproxy,William-J-Earl/cloudproxy,tmroeder/cloudproxy,cjpatton/cloudproxy,William-J-Earl/cloudproxy,William-J-Earl/cloudproxy,jethrogb/cloudproxy,tmroeder/cloudproxy,tmroeder/cloudproxy,jlmucb/cloudproxy,jlmucb/cloudproxy,cjpatton/cloudproxy,kevinawalsh/cloudproxy,William-J-Earl/cloudproxy,jlmucb/cloudproxy,tmroeder/cloudproxy,cjpatton/cloudproxy,cjpatton/cloudproxy,jethrogb/cloudproxy,jethrogb/cloudproxy,William-J-Earl/cloudproxy