Stop one lseek(2) per header fetched by m_getfld.c in common case.

[nmh] / etc / rcvdistcomps

%(void(localmbox))%(void(width))%(putaddr Resent-From: )
%(lit)%(formataddr{addresses})\
%<(nonnull)%(void(width))%(putaddr Resent-To: )\n%>