[exim] Ustrcpy

Looks like local_scan API is broken again in +fixes.

mytypes.h is included from local_scan.h. It defines Ustrcpy as a macro
in terms of __Ustrcpy which is an inline function in functions.h.
functions.h is of course not included either in local_scan.h or
mytypes.h, and AFAIK is not part of the API.

--
Ian