Revision 208899

MFC r197608:

The first 96 bytes may not be zeroes. It can contain trivial boot
code that merely emits an error and waits for a key press before
rebooting. The error being that extended partitions are not
bootable. The origin is presumed to be Windows 2000; Windows XP
does not do this...

For now, ignore the first 96 bytes when checking that the EBR is
(for the most part) all zeroes.

Tested by:	Mario Lobo <mlobo at digiart.art.br>
		Dieter <dieterbsd at engineer.com>
PR:		kern/141235
Reviewed by:	marcel
Approved by:	kib (mentor)
Approved by:	re (bz)