Convert GIT_SHA1_RAWSZ used for allocation to GIT_MAX_RAWSZ

Since we will likely be introducing a new hash function at some point,
and that hash function might be longer than 20 bytes, use the constant
GIT_MAX_RAWSZ, which is designed to be suitable for allocations, instead
of GIT_SHA1_RAWSZ.  This will ease the transition down the line by
distinguishing between places where we need to allocate memory suitable
for the largest hash from those where we need to handle the current
hash.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wt-status.h

@@ -80,7 +80,7 @@ struct wt_status {
 	int hints;
 
 	enum wt_status_format status_format;
-	unsigned char sha1_commit[GIT_SHA1_RAWSZ]; /* when not Initial */
+	unsigned char sha1_commit[GIT_MAX_RAWSZ]; /* when not Initial */
 
 	/* These are computed during processing of the individual sections */
 	int commitable;