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/PubUtilLib/plNetClient/plNetCliAgeJoiner.cpp

@@ -408,7 +408,7 @@ bool plNCAgeJoiner::MsgReceive (plMessage * msg) {
         else if (unsigned ageVaultId = NetCommGetAge()->ageVaultId) {
             // Download the age vault
             VaultDownload(
-                L"AgeJoin",
+                "AgeJoin",
                 ageVaultId,
                 AgeVaultDownloadCallback,
                 this,