fix a number of assuptions that a long could hold an inum
* libguile/bytevectors.c:
* libguile/goops.c:
* libguile/instructions.c:
* libguile/numbers.c:
* libguile/random.c:
* libguile/read.c:
* libguile/vm-i-scheme.c: Fix a number of assumptions that a long could
hold an inum. This is not the case on platforms whose void* is larger
than their long.
* libguile/numbers.c (scm_i_inum2big): New helper, only implemented for
sizeof(void*) == sizeof(long); produces a compile error on other
platforms. Basically gmp doesn't have a nice interface for converting
between mpz values and intmax_t.