set /sim/fg-home in analogy to /sim/fg-root. This is useful for various

scripts that load/write user specific data that shouldn't go to PWD, and
can't go to $FG_ROOT (due to permissions and clean separation of 'official'
data and local modifications)

src/Main/fg_init.cxx

@@ -607,6 +607,7 @@ bool fgInitConfig ( int argc, char **argv ) {
         SGPath config( homedir );
         config.append( ".fgfs" );
 #endif
+        fgSetString("/sim/fg-home", config.c_str());
         config.append( "autosave.xml" );
         SG_LOG(SG_INPUT, SG_INFO, "Reading user settings from autosave.xml");
         try {