Prevent release packages from being generated in NuGet pkg dir

[caesay]

People often navigate to the %userprofile%\.nuget\... Squirrel directory, and run Squirrel.exe from there. They often also do not provide a release dir, meaning resulting packages are created inside the NuGet directory. In this case, we should default to a temp directory, or maybe a default directory like %userprofile%\SquirrelClowd.

When we use this default directory should also print a warning showing the folder we used and mentioning the -r argument.

I think we should do this any time CurrentDirectory == BaseDirectory, so this will also impact people who have downloaded the tools from GH, and extracted the zip in their downloads directory.

[caesay]

This is no longer relevant as in 3.x the only way to run the Squirrel package generator is through the csq tool.