Adding ToString override to .NET Platform class

Fixes issue #580.

Author: jimevans

dotnet/src/webdriver/Firefox/Internal/Executable.cs

@@ -70,7 +70,7 @@ public Executable(string userSpecifiedBinaryPath)
             }
 
             throw new WebDriverException("Cannot find Firefox binary in PATH or default install locations. " +
-                "Make sure Firefox is installed. OS appears to be: " + Platform.CurrentPlatform);
+                "Make sure Firefox is installed. OS appears to be: " + Platform.CurrentPlatform.ToString());
         }
         #endregion
 

dotnet/src/webdriver/Platform.cs

@@ -204,5 +204,14 @@ public bool IsPlatformType(PlatformType compareTo)
 
             return platformIsType;
         }
+
+        /// <summary>
+        /// Returns the string value for this platform type.
+        /// </summary>
+        /// <returns>The string value for this platform type.</returns>
+        public override string ToString()
+        {
+            return this.platformTypeValue.ToString();
+        }
     }
 }