Issue #41 - Bring method of determining IE version up to date

src/shared/Registry.h

+#include <string>
+#include <Windows.h>
+
+namespace AdblockPlus
+{
+  /**
+   * An open key in the system registry.
+   */
+  class Registry_Key
+  {
+    /**
+     * Handle to an open registry key.
+     */
+    HKEY key;
+
+    /**
+     * Flag whether the registry key is predefined or not.
+     *
+     * Predefined key values are considered "always open" and should not be closed in the destructor.
+     */
+    bool is_predefined;
+
+  public:
+    /**
+     * Enumeration for predefined root keys.
+     */
+    enum class Predefined
+      : unsigned int
+    {
+      HKCR = 0,   // HKEY_CLASSES_ROOT
+      HKCC,       // HKEY_CURRENT_CONFIG
+      HKCU,       // HKEY_CURRENT_USER
+      HKLM,       // HKEY_LOCAL_MACHINE
+      HKU         // HKEY_USERS
+    };
+
+    /**
+     * Constructor to open a key under one of the predefined roots.
+     * Opens the key with read-only access.
+     *
+     * Because the invariant of this class is that the underlying registry key is open,
+     *   this constructor throws if 'key_name' is not found.
+     */
+    Registry_Key(Predefined root, std::wstring key_name);
+
+    /**
+     * Constructor for one of the predefined roots.
+     */
+    Registry_Key(Predefined root);
+
+    /**
+     * Destructor closes the key if it's not a predefined one.
+     */
+    ~Registry_Key();
+
+    /**
+     * Retrieve a value from a name-value pair within the present key.
+     *
+     * Throws if the name is not found within the dictionary.
+     * Throws if the name is found but is not a string.
+     */
+    std::wstring value_wstring(std::wstring name) const;
+  };
+}
+