Depend on virtual/perl-Math-BigInt instead of perl-core/Math-BigInt

(Portage version: 2.2.8-r1/cvs/Linux x86_64, signed Manifest commit with key 94BFDF4484AD142F)
Fix bug #515680 - Bump eid-mw, also commit live ebuild. Thanks to Vincent Hardy

(Portage version: 2.2.8-r1/cvs/Linux x86_64, signed Manifest commit with key 0x2EDD52403B68AF47)