Move to a model with a unified request object.

Move to a model with a unified request object.
Constructor takes a bool to signify that it is either a cpu_request or not a cpu_request.
When accedding variables of a cpu_request it asserts that it is a cpu_request.
It also asserts that a value being read has been written at some point in time prior (not gaurnteeing it is up to date, but it was at least written before read).

There is also a isCpuReq() function to determine if this is a cpu_request.  It should be called before accesing a cpu_request only variable.

SConscript:
    Add compilation support for request.cc
arch/alpha/tlb.cc:
arch/alpha/tlb.hh:
cpu/cpu_exec_context.hh:
cpu/exec_context.hh:
cpu/simple/cpu.cc:
cpu/simple/cpu.hh:
dev/io_device.cc:
mem/page_table.cc:
mem/page_table.hh:
mem/port.cc:
    Update for unified request object and accessor functions.
mem/request.hh:
    Remove CpuRequest, make it a unified object.  Make variables private with accessor functions.

    May want to move things from .cc file into header (usually a assert() and either returning a value, or writting two).

--HG--
extra : convert_revision : f1e45cc490dadc7a418634539b03c3e72684a6e3