object-store.h: move struct object_info from cache.h
Move struct object_info, and a few related #define's from cache.h to
object-store.h.
A surprising effect of this change is that replace-object.h, which
includes object-store.h, now needs to directly include cache.h since
that is where read_replace_refs is declared and that variable is used
in one of its inline functions. The next commit will move that
declaration and fix that unfortunate new direct inclusion of cache.h.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>