stop using /sim/terrasync/scenery-dir, fix scenery path order

Having non-Nasal-readable scenery paths breaks things
(The property continues to exist, but is now from-C++-to-Nasal only)

src/Main/fg_commands.cxx

@@ -1347,7 +1347,7 @@ do_set_scenery_paths(const SGPropertyNode* arg)
 {
   globals->clear_fg_scenery();
   
-  std::string terrasyncPath(fgGetString("/sim/terrasync/scenery-dir"));
+  std::string terrasyncPath(globals->get_terrasync_dir().local8BitStr());
   bool seenTerrasyncPath = false;
   
   simgear::PropertyList paths = arg->getChildren("path");

src/Main/globals.cxx

@@ -418,6 +418,25 @@ void FGGlobals::clear_fg_scenery()
 
 }
 
+void FGGlobals::set_terrasync_dir(const SGPath &path)
+{
+  if (terrasync_dir.realpath() != SGPath(fgGetString("/sim/terrasync/scenery-dir")).realpath()) {
+    // if they don't match, /sim/terrasync/scenery-dir has been set by something else
+    SG_LOG(SG_GENERAL, SG_ALERT, "/sim/terrasync/scenery-dir is no longer stored across runs: if you wish to keep using a non-standard Terrasync directory, use --terrasync-dir or the launcher's settings");
+  }
+  SGPath abspath(path.realpath());
+  terrasync_dir = abspath;
+  // deliberately not a tied property, for fgValidatePath security
+  // write-protect to avoid accidents
+  SGPropertyNode *n = fgGetNode("/sim/terrasync/scenery-dir", true);
+  n->setAttribute(SGPropertyNode::WRITE, true);
+  n->setStringValue(abspath.utf8Str());
+  n->setAttribute(SGPropertyNode::WRITE, false);
+  // don't add it to fg_scenery yet, as we want it ordered after explicit --fg-scenery
+}
+
+
+
 void FGGlobals::set_catalog_aircraft_path(const SGPath& path)
 {
     catalog_aircraft_dir = path;

src/Main/globals.hxx

@@ -104,6 +104,8 @@ private:
     
     // Users home directory for data
     SGPath fg_home;
+    //Terrasync directory
+    SGPath terrasync_dir;
 
     // Roots of FlightGear scenery tree
     PathList fg_scenery;
@@ -219,6 +221,9 @@ public:
     const SGPath &get_fg_home () const { return fg_home; }
     void set_fg_home (const SGPath &home);
 
+    const SGPath &get_terrasync_dir () const { return terrasync_dir; }
+    void set_terrasync_dir (const SGPath &path);
+
     const PathList &get_fg_scenery () const { return fg_scenery; }
     const PathList &get_unmangled_fg_scenery () const { return unmangled_fg_scenery; }
     const PathList &get_extra_read_allowed_paths () const { return extra_read_allowed_paths; }

src/Main/main.cxx

@@ -125,7 +125,7 @@ static void initTerrasync()
 {
     // add the terrasync root as a data path so data can be retrieved from it
     // (even if we are in read-only mode)
-    std::string terraSyncDir(fgGetString("/sim/terrasync/scenery-dir"));
+    SGPath terraSyncDir(globals->get_terrasync_dir());
     globals->append_data_path(terraSyncDir);
     
     if (fgGetBool("/sim/fghome-readonly", false)) {

src/Main/options.cxx

@@ -860,8 +860,7 @@ static int
 fgOptTerrasyncDir( const char *arg )
 {
     SGPath p = SGPath::fromLocal8Bit(arg);
-    globals->append_fg_scenery(p, true);
-    fgSetString("/sim/terrasync/scenery-dir", p.utf8Str());
+    globals->set_terrasync_dir(p);
     return FG_OPTIONS_OK;
 }
 
@@ -2377,7 +2376,7 @@ OptionResult Options::processOptions()
   }
 
 // download dir fix-up
-    SGPath downloadDir = SGPath::fromUtf8(fgGetString("/sim/paths/download-dir"));
+    SGPath downloadDir = SGPath::fromUtf8(valueForOption("download-dir"));
     if (downloadDir.isNull()) {
         downloadDir = defaultDownloadDir();
         SG_LOG(SG_GENERAL, SG_INFO, "Using default download dir: " << downloadDir);
@@ -2390,7 +2389,7 @@ OptionResult Options::processOptions()
     }
 
 // terrasync directory fixup
-    SGPath terrasyncDir = SGPath::fromUtf8(fgGetString("/sim/terrasync/scenery-dir"));
+    SGPath terrasyncDir = globals->get_terrasync_dir();
   if (terrasyncDir.isNull()) {
       SGPath p(downloadDir);
       p.append("TerraSync");
@@ -2402,7 +2401,7 @@ OptionResult Options::processOptions()
       }
 
 	  SG_LOG(SG_GENERAL, SG_INFO, "Using default TerraSync: " << terrasyncDir);
-      fgSetString("/sim/terrasync/scenery-dir", p.utf8Str());
+      globals->set_terrasync_dir(p);
   } else {
       SG_LOG(SG_GENERAL, SG_INFO, "Using explicit TerraSync dir: " << terrasyncDir);
   }

src/Scenery/tilemgr.cxx

@@ -174,7 +174,7 @@ void FGTileMgr::reinit()
     _options->setPluginStringData("SimGear::FG_ROOT", globals->get_fg_root().local8BitStr());
     
     if (_terra_sync) {
-      _options->setPluginStringData("SimGear::TERRASYNC_ROOT", fgGetString("/sim/terrasync/scenery-dir"));
+      _options->setPluginStringData("SimGear::TERRASYNC_ROOT", globals->get_terrasync_dir().local8BitStr());
     }
     
     if (!_disableNasalHooks->getBoolValue())