VS: Add static method to get the base of the registry

Source/cmGlobalVisualStudioGenerator.cxx

@@ -32,10 +32,17 @@ cmGlobalVisualStudioGenerator::~cmGlobalVisualStudioGenerator()
 
 //----------------------------------------------------------------------------
 std::string cmGlobalVisualStudioGenerator::GetRegistryBase()
+{
+  return cmGlobalVisualStudioGenerator::GetRegistryBase(
+    this->GetIDEVersion());
+}
+
+//----------------------------------------------------------------------------
+std::string cmGlobalVisualStudioGenerator::GetRegistryBase(
+  const char* version)
 {
   std::string key = "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\";
-  key += this->GetIDEVersion();
-  return key;
+  return key + version;
 }
 
 //----------------------------------------------------------------------------

Source/cmGlobalVisualStudioGenerator.h

@@ -65,6 +65,9 @@ public:
   /** Get the top-level registry key for this VS version.  */
   std::string GetRegistryBase();
 
+  /** Get the top-level registry key for the given VS version.  */
+  static std::string GetRegistryBase(const char* version);
+
   /** Return true if the generated build tree may contain multiple builds.
       i.e. "Can I build Debug and Release in the same tree?" */
   virtual bool IsMultiConfig() { return true; }