In 2.5.7 there is a thinko in the allocation and initialisation
of the fs-private superblock for ext2.  It's passing the wrong type
to the sizeof operator (which of course gives the wrong size)
when allocating and clearing the memory.

Lesson for the day: this is one of the reasons why this idiom:

	some_type *p;

	p = malloc(sizeof(*p));
	...
	memset(p, 0, sizeof(*p));

is preferable to

	some_type *p;

	p = malloc(sizeof(some_type));
	...
	memset(p, 0, sizeof(some_type));

I checked the other filesystems.  They're OK (but idiomatically
impure).  I've added a couple of defensive memsets where
they were missing.