Update ResGen Serialization Compat for RTM and U1

When reverting the CodeFormatter private field name changes, the
Dependencies class was missed. This causes an incompatability going from
VS2015 Update 1 back to RTM and causes a null ref. This change fixes the
compat issue (rename the field) and updates the serialization version to
ensure U1 -> U2 works as expected.

src/XMakeTasks/Dependencies.cs

@@ -26,7 +26,7 @@ internal class Dependencies
         /// Hashtable of other dependency files.
         /// Key is filename and value is DependencyFile.
         /// </summary>
-        private Hashtable _dependencies = new Hashtable();
+        private Hashtable dependencies = new Hashtable();
 
         /// <summary>
         /// Look up a dependency file. Return null if its not there.
@@ -35,7 +35,7 @@ internal class Dependencies
         /// <returns></returns>
         internal DependencyFile GetDependencyFile(string filename)
         {
-            return (DependencyFile)_dependencies[filename];
+            return (DependencyFile)dependencies[filename];
         }
 
 
@@ -46,7 +46,7 @@ internal DependencyFile GetDependencyFile(string filename)
         /// <returns></returns>
         internal void AddDependencyFile(string filename, DependencyFile file)
         {
-            _dependencies[filename] = file;
+            dependencies[filename] = file;
         }
 
         /// <summary>
@@ -56,15 +56,15 @@ internal void AddDependencyFile(string filename, DependencyFile file)
         /// <returns></returns>
         internal void RemoveDependencyFile(string filename)
         {
-            _dependencies.Remove(filename);
+            dependencies.Remove(filename);
         }
 
         /// <summary>
         /// Remove all entries from the dependency table.
         /// </summary>
         internal void Clear()
         {
-            _dependencies.Clear();
+            dependencies.Clear();
         }
     }
 }

src/XMakeTasks/StateFileBase.cs

@@ -20,7 +20,7 @@ internal class StateFileBase
         // Current version for serialization. This should be changed when breaking changes
         // are made to this class.
         // Note: Consider that changes can break VS2015 RTM which did not have a version check.
-        private const byte CurrentSerializationVersion = 2;
+        private const byte CurrentSerializationVersion = 3;
 
         // Version this instance is serialized with.
         private byte _serializedVersion = CurrentSerializationVersion;