this time do it ourselves instead of piggybacking on TLS.
add -fno-pic to Makefile; pic code breaks our fake TLS.

still not quite but a lot better.

 * rename c/cp to cpu/proc
 * rename cpu.context to cpu.scheduler
 * fix some comments
 * formatting for printout

pdf has very good page breaks now.
would be a good copy for fall 2009.

IRQ_OFFSET -> T_IRQ0 (a trap number not an IRQ number)
T_SYSCALL 0x30 -> 0x40 (move out of IRQ range)

move the SYSCALL number up, so does not overlap the IRQ traps.

few naming nits.