Fix warnings in the build

[davidfowl]

@ChengTian We should also turn on warnings as errors once this is fixed.

[ChengTian]

@davidfowl I tested kpm build and seems it can generate correct warnings. Which specific part needs to be fixed?

[davidfowl]

Not that our build has warnings :). Building KRuntime shows warnings which is bad. We need to fix them

[ChengTian]

I see: ) I will be working on them.

[ChengTian]

@davidfowl , XmlUtility class defined in
Microsoft.Framework.PackageManager / NuGet / Core / Utility / XmlUtility.cs
conflicts with the one defined in
Microsoft.Framework.Runtime / NuGet / Utility / XmlUtility.cs
The two files have almost identical contents. Do we want to move XmlUtility.cs to a common project which can be shared across all projects?

[davidfowl]

Keep it in the runtime and nuke the one in PackageManager