Test export private keys in C.

Result : fails.
Reason : password callback is never called.

With default pinentry mode, the password is requested normally 
and the private key is exported. But this can't be done on a web server.

Enclosed in #ifdef DEVTIME.

GpgMECWorker.h

@@ -31,6 +31,20 @@ public:
      */
     bool DeleteKey(const char * fpr, bool secret, GpgME::Error& e);
 
+#ifdef DEVTIME
+    /**
+     * Status : testing
+     * \n Result : fails to export a private key
+     * \n Reason : passphrase callback is never called
+     * \n With default pinentry mode, the password is requested normally 
+     * and the private key is exported. But this can't be done on a web server.
+     * @param fpr
+     * @param e
+     * @return 
+     */
+    bool ExportPrivateKey(const char* fpr, GpgME::Error& e);
+#endif
+
 private:
     gpgme_ctx_t c_ctx;
 };