Fix GetRelativePath with different volumes

src/Microsoft.Dnx.Runtime/NuGet/Utility/PathUtility.cs

@@ -86,6 +86,12 @@ public static string GetRelativePath(string path1, string path2, char separator)
             if (Microsoft.Dnx.Runtime.RuntimeEnvironmentHelper.IsWindows)
             {
                 compare = StringComparison.OrdinalIgnoreCase;
+                // check if paths are on the same volume
+                if (!string.Equals(Path.GetPathRoot(path1), Path.GetPathRoot(path2)))
+                {
+                    // on different volumes, "relative" path is just path2
+                    return path2;
+                }
             }
             else
             {

test/Microsoft.Dnx.Runtime.Tests/PathUtilityFacts.cs

@@ -69,7 +69,10 @@ public static IEnumerable<object[]> FolderPaths
                         new object[] { "", "C:/folder/app", "C:/folder/app" },
                         new object[] { "app/", "C:/folder/app", "C:/folder/app/" },
                         new object[] { "../diff/app/", "C:/folder/app", "C:/diff/app/" },
-                        new object[] { "../folder1/file", "C:\\folder\\file", "C:\\folder1\\file" }
+                        new object[] { "../folder1/file", "C:\\folder\\file", "C:\\folder1\\file" },
+                        new object[] { "H:\\folder\\file", "C:\\folder\\file", "H:\\folder\\file" },
+                        new object[] { "folder/file", "C:\\", "C:\\folder\\file" },
+                        new object[] { "..\\", "C:\\folder\\file", "C:\\" }
                     });
                 }
                 else