gentoo perl update problem

problem description

Performing a world update(emerge -uavND world) on gentoo is failing with the error messages below.

Error

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

dev-lang/perl:0

(dev-lang/perl-5.18.2::gentoo, ebuild scheduled for merge) pulled in by
   =dev-lang/perl-5.18* required by (virtual/perl-Perl-OSType-1.3.0::gentoo, ebuild scheduled for merge)
   (and 4 more with the same problem)
 
(dev-lang/perl-5.16.3::gentoo, installed) pulled in by
   dev-lang/perl:0/5.16=[-build(-)] required by (dev-vcs/git-1.8.5.3::gentoo, installed)
   dev-lang/perl:0/5.16=[-build(-)] required by (dev-vcs/subversion-1.8.5::gentoo, installed)
   =dev-lang/perl-5.16* required by (virtual/perl-digest-base-1.170.0-r1::gentoo, installed)