Make the to_number function work better.

Make the to_number function work better.

base/str.cc:
    Make some fixes for the to_number function.
    Fix overflow calculation for maximum decimal value.
    (Note: minimum decimal value for signed numbers does not
    work correctly, e.g. it will overflow on -128 for a signed char
    though -127 will work)
    Fix overflow calculation for hex values being converted into
    signed types
    Fix up the debugging stuff a little to make sure the values are
    always printed as numbers.
test/strnumtest.cc:
    using namespace std for g++ 3

--HG--
extra : convert_revision : b00bb1296c85c3d64d8864283c9374e1563bfa31