Fix /property:OS=Unix build of System.Console

Some resource strings got lost in the move to GitHub.  There was also an inconsistency with the available NuGet packages and where SafeHandle lives.
Fix vector tests warnings about obsolete Marshal.SizeOf

The System.Numerics.Vectors tests were causing build warnings like the following:

Vector2Tests.cs(15,29): warning CS0618: 'System.Runtime.InteropServices.Marshal.SizeOf(System.Type)' is obsolete: 'SizeOf(Type) may be unavailable in future releases. Instead, use SizeOf<T>().

This changes does exactly that.
Add System.Runtime.Handles reference to System.Console
Merge pull request #221 from stephentoub/fix_vector_test_warnings

Fix vector tests warnings about obsolete Marshal.SizeOf
Merge pull request #220 from stephentoub/fix_console_unix

Fix /property:OS=Unix build of System.Console