Update Math::BigInt to CPAN version 1.992

Update Math::BigInt to CPAN version 1.992

dist/Math-BigInt/lib/Math/BigFloat.pm:
 - Increment version number.

dist/Math-BigInt/lib/Math/BigInt.pm:
 - Increment version number.
 - Make from_hex(), from_oct(), and behave more like hex() and oct()
   in the Perl core, and make from_bin() consistent with from_hex()
   and from_oct(). This is related to RT #58954.

dist/Math-BigInt/lib/Math/BigInt/Calc.pm:
 - Increment version number.
 - Make _rem() modify first input arg always, not just sometimes.
 - Make _modinv() more consistent with the _modinv() method in other
   libraries (Math::BigInt::GMP, etc.)
 - In _nok(), use symmetry property nok(n,k) = nok(n,n-k). This cuts
   computation time tremendously when n and k are large.
 - In _gcd(), quickly handle zero cases, avoid code duplication, and
   always modify the first input argument in-place.
 - Clean up code and add more code comments.
 - Fix typos.

dist/Math-BigInt/lib/Math/BigInt/CalcEmu.pm:
 - Increment version number.

dist/Math-BigInt/t/bigintpm.inc:
 - Modify tests to something that still fails.

dist/Math-BigInt/t/upgrade.inc:
 - Modify tests to something that still fails.