Allow math on CheckedInt-derived ParamValue classes w/o

Allow math on CheckedInt-derived ParamValue classes w/o
losing type information.

python/m5/config.py:
    Allow math on CheckedInt-derived ParamValue classes w/o
    losing type information.
    - Make CheckedInt derive from NumericParamValue, and *not*
    multiply inherit from long
    - Move CheckedInt bounds check to _check() hook so we can
    call it when value is updated (not just in constructor)
python/m5/convert.py:
    - make toInteger() return a long, making toLong() unnecessary
    - toMemorySize should return long rather than float

--HG--
extra : convert_revision : c1cf5e15b9ff35d9b573dd545e076fe68afef989