Function map_error 

pub fn map_error(err: SignedWriteError) -> RedDBError

Map a SignedWriteError onto a [RedDBError] whose marker prefix is picked up by the transport-layer status mapper.

Variant	Prefix	HTTP
MissingSignatureFields	SignedWriteError:MissingSignatureFields:	400
MalformedSignerPubkey	SignedWriteError:MalformedSignerPubkey	400
MalformedSignature	SignedWriteError:MalformedSignature	400
UnknownSigner	SignedWriteError:UnknownSigner	401
RevokedSigner	SignedWriteError:RevokedSigner	401
InvalidSignature	SignedWriteError:InvalidSignature	401