mkdir: Fix created directory permissions

Previously, with -p, the specified directory and all of its parents
would be 0777&~filemask (regardless of the -m flag). POSIX says parent
directories must created as (0300|~filemask)&0777, and of course if -m
is set, the specified directory should be created with those
permissions.

Additionally, POSIX says that for symbolic_mode strings, + and - should
be interpretted relative to a default mode of 0777 (not 0).

Without -p, previously the directory would be created first with
0777&~filemask (before a chmod), but POSIX says that the directory shall
at no point in time have permissions less restrictive than the -m mode
argument.

Rather than dealing with mkdir removing the filemask bits by calling
chmod afterward, just clear the umask and remove the bits manually.

tar.c

@@ -262,7 +262,7 @@ unarchive(char *fname, ssize_t l, char b[BLKSIZ])
 		weprintf("remove %s:", fname);
 
 	tmp = estrdup(fname);
-	mkdirp(dirname(tmp));
+	mkdirp(dirname(tmp), 0777, 0777);
 	free(tmp);
 
 	switch (h->type) {