48-bit fixnums

[Bruno H. <br...@cl...>]

Hi,

I've committed a patch that allows for 48-bit fixnums on 64-bit platforms.
Noteworthy changes:

  - a new integer type 'uintV' that is the smallest integer type that can
    accomodate a nonnegative fixnum's value. Either uint32 or uint64.
  - posfixnum_to_L is gone. More precisely, it's replaced with posfixnum_to_V,
    which returns a n uintV.
  - In modules like rawsock or bdb, it is now a BUG to write

      unsigned int foo = posfixnum_to_V(check_posfixnum(STACK_0));

    because that would cause values between 2^32 and most-positive-fixnum
    to be accepted but to be truncated. As a replacement, use

      unsigned int foo = I_to_uint(check_uint(STACK_0));

Bruno