Add $tf folder to VisualStudio.gitignore

TFS 2012 creates a $tf folder for local workspaces

VisualStudio.gitignore

@@ -56,6 +56,9 @@ ipch/
 *.vsp
 *.vspx
 
+# TFS 2012 Local Workspace
+$tf/
+
 # Guidance Automation Toolkit
 *.gpState