Too many iterators, all the same.
a couple of macros are better than that much duplication

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

Also, a longstanding, never-triggered bug got fixed.

More work need to be done for decoder iterators, and the
<future>, which is not supported in C++98

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>