* Rebase onto .NET Core 1.1
Modify `Build.psm1` and `project.json` files to use .NET Core 1.1.
.NET Core 1.1 ships with an older dotnet/cli than has currently been used,
so we revert to use case-sensitive directory names for dependencies.
.NET Core 1.1 is a pre-requisite for supporting Fedora 24.
* PSReadLine: Bump major version of PSReadline to 6.0.0-*
* Microsoft.PowerShell.Commands.Utility: Bump major version of Microsoft.CodeAnalysis.Csharp
* Microsoft.PowerShell.SDK: Revert attempt to import netcoreapp1.1 instead of dnxcore
* build.psm1: Restore ability to specify version of dotnet-install.sh
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