Allow exporting secret keys.

Requests the passphrase with a popup.

As from GPGME 1.15.0, the loopback pinentry is functional when exporting secret keys. It works fine when the exact passphrase is provided. If it's a wrong passphrase, GPGME does not generate an ::Error, but the app crashes with 'free(): double free detected in tcache 2'.

Hence, this patch cannot be committed to master.

Status : dangerous
Result : works and works not
Reason : a wrong passphrase means a crash

GpgMEWorker.cpp

@@ -308,8 +308,6 @@ const Error GpgMEWorker::CreateSubKey(GpgME::Key& k,
     return e;
 }
 
-#ifdef DEVTIME
-
 const Error GpgMEWorker::ExportPrivateKey(const char * pattern, string& buffer,
                                           const string& passphrase)
 {
@@ -324,14 +322,13 @@ const Error GpgMEWorker::ExportPrivateKey(const char * pattern, string& buffer,
     uint flags = Context::ExportSecret;
 
     Error e = ctx->exportPublicKeys(pattern, kData, flags);
-    buffer = kData.toString(); // Empty
+    buffer = kData.toString();
 
     delete ppp;
     delete ctx;
 
     return e;
 }
-#endif
 
 const Error GpgMEWorker::ExportPublicKey(const char* pattern, string& buffer)
 {