Make a new stat type of Value which is a scalar stat that

Make a new stat type of Value which is a scalar stat that
proxies for a real C/C++ scalar value or scalar functor.
This replaces the scalar() and functor() terms that were
previously used in formulas.  This helps when dumping
statistics because the formulas are not supposed to change.

cpu/base_cpu.cc:
    Add a number of cycles stat to the cpu object that tracks the
    number of cycles that the cpu has executed.  This starts to pave
    the way for cpu cycles being different from event ticks.
cpu/base_cpu.hh:
    provide a functor for calculating all simulated instructions
    of all CPUs and a virtual function for determining that number.
    To deal with the change from functor() to Value::functor()
cpu/simple_cpu/simple_cpu.cc:
    simTicks -> numCycles
    numInsts is now a real Scalar stat, not a Formula
cpu/simple_cpu/simple_cpu.hh:
    numInsts is now a real Scalar stat, not a Formula
    count all instructions
sim/stat_control.cc:
    simInsts, simTicks, hostMemory, and hostSeconds are no
    longer Statistics::Formula but rather Statistics::Value
    add new stat for tick frequency
sim/stats.hh:
    don't need everything to be extern.
test/Makefile:
    Make stuff work a tad bit better
test/stattest.cc:
    test out Statistics::Value

--HG--
extra : convert_revision : c812e8baa2b17c08abf3a68ed1e1125dc6f2cfb4