Moved creation of symlink to postFixup phase.
Moved creation of symlink to postFixup phase.

This, together with a check if the symlink is necessary,
should prevent the occurrence of dangling symlinks.

svn path=/nixpkgs/trunk/; revision=24232

NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,triton/triton,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,triton/triton,NixOS/nixpkgs,SymbiFlow/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,triton/triton,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,SymbiFlow/nixpkgs,triton/triton,NixOS/nixpkgs,NixOS/nixpkgs