Fix off-by-one in apathmax() as the path is relative to "/"

1) Use size_t * instead of long *
2) Fallback to PATH_MAX instead of BUFSIZ
3) Header cleanup

libutil/apathmax.c

@@ -1,22 +1,22 @@
 /* See LICENSE file for copyright and license details. */
 #include <errno.h>
-#include <stdio.h>
-#include <stdlib.h>
+#include <limits.h>
 #include <unistd.h>
 
 #include "../util.h"
 
 void
-apathmax(char **p, long *size)
+apathmax(char **p, size_t *size)
 {
 	errno = 0;
-
 	if ((*size = pathconf("/", _PC_PATH_MAX)) < 0) {
 		if (errno == 0) {
-			*size = BUFSIZ;
+			*size = PATH_MAX;
 		} else {
 			eprintf("pathconf:");
 		}
+	} else {
+		(*size)++;
 	}
 	*p = emalloc(*size);
 }