Convert vault tree printing to plString

After hacking the old to just barely use plString, I received some UTF-8
asserts. So, that seemed like a good excuse to convert the whole mess to
plString. Note that the output is now saved in VaultClient.log. This
should help with getting some of the chaos out of OLD_ASYNC_LOG.log

Sources/Plasma/FeatureLib/pfPython/cyMisc.cpp

@@ -2932,7 +2932,7 @@ void cyMisc::ForceVaultNodeUpdate(unsigned nodeId)
 void cyMisc::VaultDownload(unsigned nodeId)
 {
     VaultDownloadAndWait(
-        L"PyVaultDownload",
+        "PyVaultDownload",
         nodeId,
         nil,
         nil