vcs-svn: use constcmp instead of prefixcmp

Since the length of t is already known, we can simplify a little by
using memcmp() instead of strncmp() to carry out a prefix comparison.
All nearby code already does this.

Noticed in the standalone svn-dump-fast-export project which has not
needed to implement prefixcmp() yet.

Signed-off-by: David Barr <davidbarr@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

vcs-svn/svndump.c

@@ -361,7 +361,7 @@ void svndump_read(const char *url)
 			reset_rev_ctx(atoi(val));
 			break;
 		case sizeof("Node-path"):
-			if (prefixcmp(t, "Node-"))
+			if (constcmp(t, "Node-"))
 				continue;
 			if (!constcmp(t + strlen("Node-"), "path")) {
 				if (active_ctx == NODE_CTX)