libutil/recurse: Use a single path buffer, and directory fd

This way, we don't use PATH_MAX bytes on the stack per path component,
and don't have to keep copying the complete path around.

mv.c

@@ -2,6 +2,7 @@
 #include <sys/stat.h>
 
 #include <errno.h>
+#include <fcntl.h>
 #include <stdio.h>
 
 #include "fs.h"
@@ -21,7 +22,7 @@ mv(const char *s1, const char *s2, int depth)
 		cp_aflag = cp_rflag = cp_pflag = 1;
 		cp_follow = 'P';
 		cp(s1, s2, depth);
-		recurse(s1, NULL, &r);
+		recurse(AT_FDCWD, s1, NULL, &r);
 		return (mv_status = cp_status || rm_status);
 	}
 	mv_status = 1;