Typechecking errors with large integers and sprintf("%c").

The testsuite currently fails with:

Doing tests in testsuite (12091 tests, pid 29825)
Fri Mar 13 16:28:53 2020: Thread.Thread(0x7fced9367700) at 900
testsuite:2: Soft cast of string(1: -1412597613) to string(2147483647) isn't a valid cast.
testsuite:2: Expected: string(2147483647).
testsuite:2: Got     : string(1: -1412597613).
/lhome/build/Xenofarm/client/pike-devel/medaka.roxen.com/buildtmp/Pike-v8.1-snapshot/src/testsuite.in:14918: Test 11817 (CRNL) failed.
  1: mixed a() { return "\25363274223"; }
  2: mixed b() { return  sprintf("%c", 0x1abcd7893) ; }

testsuite:2: Soft cast of string(1: 1412597613) to string(-2147483648) isn't a valid cast.
testsuite:2: Expected: string(-2147483648).
testsuite:2: Got     : string(1: 1412597613).
/lhome/build/Xenofarm/client/pike-devel/medaka.roxen.com/buildtmp/Pike-v8.1-snapshot/src/testsuite.in:14919: Test 11818 (shift 1) (CRNL) failed.
  1: mixed a() { return "\12414503555"; }
  2: mixed b() { return  sprintf("%c", -0x1abcd7893) ; }

Subresult: 41609 tests, 2 failed, 13 skipped

The cause is that the values 025363274223, 0x1abcd7893, 012414503555 and -0x1abcd7893 all are out of the 32-bit signed range of the integer type.

The easiest fix is probably just to switch the type for large integers to the generic int type.