Interoperability for different PAGE_SIZE/wordsize machines. Tested on ia64

Interoperability for different PAGE_SIZE/wordsize machines.  Tested on ia64
and i386 separately, and with ia64 client + i386 MDS/OST.

Mostly aligning structs to have 64-bit fields aligned on 64-bit boundaries.
Remove some VFS constants and replace them with Lustre constants on the wire.
Since the MDS doesn't really open files itself, we don't need to convert from
the wire constants back to local flags at all.

Frobbing of niobufs on the targets to split them into PAGE_SIZE chunks (this
may be a problem on large PAGE_SIZE servers with small PAGE_SIZE clients,
not sure yet).

I have tested and this appears to be compatible with old filesystems.
At worst we should only need another --write_conf on the MDS.

b=686, b=1821, b=1343, b=2042