adding newfs_ext2fs and mount_ext2fs to ramdisk flist

Hello,

It's possible to run NetBSD/xen in the DomUs of many hosting providers
which disavow any NetBSD support.  I've added mount_ext2fs and
newfs_ext2fs to my installation ramdisk to create and mount the
disklabel slice where pv-grub looks to find its configuration file and
kernels.  Yes, pv-grub does have some ffs support, but it doesn't seem
to able to cope with filesystems created with -O2 (I was going to
write UFS2, but the whole ffs2 vs ufs2 nomenclature and taxonomy
confuses me).

At any rate, this is an extremely simple change that makes life
easier.  Can we do it?

Regards,

--Blair