DelaySign with a public key.

[antero-lukkonen]

Background:
It is not uncommon to have a assembly signing remote server that holds the private keys and public keys distributed to the developers to be used for delay signing.
Currently if specifying /delaysign and /keyfile=mypublic.snk is used with ilrepack, it fails with an error:

System.ArgumentException: Unable to obtain public key for StrongNameKeyPair.
at System.Reflection.StrongNameKeyPair.ComputePublicKey()
at System.Reflection.StrongNameKeyPair.get_PublicKey()
at ILRepacking.Steps.SigningStep.Perform()
at ILRepacking.ILRepack.Repack()
at ILRepacking.Application.Main(String[] args)

Acceptance criteria:
Given: i have a key file with only a public key called mypublic.snk
When: i run ilrepack with /delaysign and /keyfile=mypublic.snk
Then: i get a delay signed assembly as a result.

[gluck]

Hi, could it be you're hitting the same issue that was mentioned in PR #146 ?
This PR hasn't been followed upon, but feel free to give it a go.

Cheers.