Initialization sequence

On boot, we jump to the "main" routine in B289 which does
very few things.

1. Set SP to PS_ADDR and IX to RS_ADDR
2. Sets HERE to RAMEND (RAMSTART+0x80).
3. Sets CURRENT to value of LATEST field in stable ABI.
4. Look for the word "BOOT" and calls it.

In a normal system, BOOT is in xcomp core (B411) and does a
few things:

1. Initialize all overrides to 0.
2. Write LATEST in BOOT C< PTR ( see below )
3. Set "C<*", the word that C< calls to (boot<).        (cont.)