pegbox: pegbus: use defined constant for IO_MMU
pegbox: kprint: make IO_TERMINAL a defined constant
pegbox: check the IO bit in the pegbus 'restore old page' code
pegbox: make it possible to increase the kernel binary beyond one page

Other vpages, like the stack and the child-stack (when forking), are now
 defined in mem.s; and the isr and ivt sections can now be relocated.
pegbox: increased size of kernel binary to two pages

The first page was nearly full; and I wanted to prove that increasing the
 size would work and not break anything.
Move the kernel LDscript into pegbox/ where it belongs

User programs (when those are possible) will need an entirely different
 linker script.