[Rd] "getOption(max.print) omitted %d entries" may be negative

[Hugh Parsonage]

In src/main/printvector.c in the definition of printVector and
printNamedVector  (and elsewhere):

Rprintf(" [ reached getOption(\"max.print\") -- omitted %d entries ]\n",
n - n_pr);

Though n - n_pr is of type R_xlen_t so may not be representable as
int. In practice negative values may be observed for long vectors.

Rprintf(" [ reached getOption(\"max.print\") -- omitted %lld entries ]\n",
n - n_pr);