Rework DateTime struct (#103)

***PUBLISH_RELEASE***
***UPDATE_DEPENDENTS***

Author: josesimoes

source/nanoFramework.CoreLibrary/System/AssemblyInfo.cs

@@ -14,4 +14,4 @@
 [assembly: AssemblyProduct("nanoFramework mscorlib")]
 [assembly: AssemblyCopyright("Copyright © nanoFramework Contributors 2017")]
 
-[assembly: AssemblyNativeVersion("100.4.8.0")]
+[assembly: AssemblyNativeVersion("100.4.9.0")]