Update to 1.6003
Update DEPENDS

Upstream changes:
2017-01-11 v1.6003 pjacklam

 * Fix syntax for required version of Math::BigInt::Lib.

 * Better checking of POD coverage.

 * Sync test files with Math-BigInt-1.999808.

2016-12-03 v1.6002 pjacklam

 * Use ExtUtils::MakeMaker rather than Module::Install in Makefile.PL

 * Don't use Devel::CheckLib. It fails on Windows even in cases where
   this distribution would build just fine.

 * Update BUGS file.

 * Remove author information in LICENSE file.

 * Inform that the TODO file is not up to date.

 * Remove INSTALL file. The information is in the README file.

2016-11-23 v1.6001 pjacklam

 * Sync test files with Math-BigInt-1.999801.

 * Correct version number in CHANGES file.

2016-11-15 v1.6000 pjacklam

 * Sync test files with Math-BigInt-1.999800.

 * Update bundled Devel::CheckLib from v1.03 to v1.07.

 * Math::BigInt::GMP is now a subclass of Math::BigInt::Lib, so remove pure
   Perl methods from Math::BigInt::GMP that are implemented in the superclass
   Math::BigInt::Lib. The methods removed are _digit(), _num(), _nok(), and
   _log_int(). The version of _log_int() implemented in Math::BigInt::GMP was
   buggy anyway.

 * Fix _check() so it doesn't give a "use of uninitialized value" warning if
   given an undefined "object".

 * Trim whitespace in all files.

 * Better use of the functionality in Test::More in t/bigintg.t.


(wen)