Function take_error 

pub fn take_error<E, DbError>(
    err: &mut Result<(), ContextError<DbError>>,
) -> Result<(), E>
where
    E: From<DbError> + FromStringError,

Take (drain) the stored context error and map it into an external error type.

This is used in multiple places (handlers/frames) to avoid duplicating the mem::replace + match ContextError boilerplate.