(chocolateyGH-1400) API - Ensure one instance of GetChocolatey

Surround `Lets.GetChocolatey` with a mutex to ensure only one instance
of `GetChocolatey` is created. There was an issue when accessing the
Chocolatey API, in that you could have multiple threads creating an
instance of `GetChocolatey` at the same time and confusing some of the
setup, causing things to fail. Instead of multiple instances, there
should be a singular instance of `GetChocolatey` .

src/chocolatey/GetChocolatey.cs

@@ -29,6 +29,7 @@ namespace chocolatey
     using infrastructure.extractors;
     using infrastructure.logging;
     using infrastructure.registration;
+    using infrastructure.synchronization;
     using resources;
     using Assembly = infrastructure.adapters.Assembly;
     using IFileSystem = infrastructure.filesystem.IFileSystem;
@@ -40,12 +41,20 @@ namespace chocolatey
     /// </summary>
     public static class Lets
     {
-        public static GetChocolatey GetChocolatey()
+        private static readonly GetChocolatey _chocolatey = GlobalMutex.enter(() => set_up(), 5);
+
+        private static GetChocolatey set_up()
         {
             add_assembly_resolver();
+
             return new GetChocolatey();
         }
 
+        public static GetChocolatey GetChocolatey()
+        {
+            return _chocolatey;
+        }
+
         private static ResolveEventHandler _handler = null;
 
         private static void add_assembly_resolver()