Add wxSecretStore

Add a new class allowing to store passwords and other sensitive information
using the OS-provided facilities.

Add implementations for all the main platforms, documentation and a new sample
(which contains an ad hoc unit test as the real unit test for this class would
probably be a bad idea as it wouldn't run in non-interactive contexts and
could show OS level dialog boxes if it did).

include/wx/gtk/private/error.h

@@ -31,6 +31,12 @@ public:
         return &m_error;
     }
 
+    // Check if any error actually occurred.
+    operator bool() const
+    {
+        return m_error != NULL;
+    }
+
     wxString GetMessage() const
     {
         return wxString::FromUTF8(m_error->message);

include/wx/gtk/setup0.h

@@ -434,6 +434,13 @@
 // Recommended setting: 1 (but may be safely disabled if you don't use it)
 #define wxUSE_FSVOLUME      1
 
+// Use wxSecretStore class for storing passwords using OS-specific facilities.
+//
+// Default is 1
+//
+// Recommended setting: 1 (but may be safely disabled if you don't use it)
+#define wxUSE_SECRETSTORE   1
+
 // Use wxStandardPaths class which allows to retrieve some standard locations
 // in the file system
 //