Slight simplification of copyuvm.  We could simplify other things now that processes are contiguous, but we'd have to think harder about the error paths.

kinit() knows about end and PHYSTOP
map all of kernel read/write (rather than r/o instructions)
thanks, austin

do not keep sorted contiguous free list

increase PHYSTOP

put an invalid page below the stack
have fork() handle invalid pages

find out the hard way why user and kernel must have separate segment descriptors

fix corner cases with alignment when mapping kernel ELF file

replace jstack with asm()s

(maybe this never worked, but it works now)