git-write-tree writes garbage on sparc64
git-write-tree writes garbage on sparc64

In the "next" branch, write_index_ext_header() writes garbage on a
64-bit big-endian machine; the written index file will be unreadable.
I noticed this on NetBSD/sparc64. Reproducible with:

$ git init-db
$ :>file
$ git-update-index --add file
$ git-write-tree
$ git-update-index
error: index uses  extension, which we do not understand
fatal: index file corrupt

Signed-off-by: Dennis Stosberg <7965a665163253a12f43312bf69d07012a113a2a@stosberg.net>
Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git