simgear/misc/sg_path.*: added SGPath::makeLink(), for making softlinks.

Note that on Windows there is no implementation yet and it always returns
false.

simgear/misc/sg_path.cxx

@@ -1108,3 +1108,15 @@ bool SGPath::touch()
     _cached = false;
     return true;
 }
+
+bool SGPath::makeLink(const std::string& destination)
+{
+    #ifdef SG_WINDOWS
+    return false;
+    #else
+    if (symlink(destination.c_str(), c_str())) {
+        return false;
+    }
+    return true;
+    #endif
+}

simgear/misc/sg_path.hxx

@@ -289,6 +289,11 @@ public:
      */
     bool touch();
     
+    /**
+     * Create a link with this path that points to <destination>.
+     */
+    bool makeLink(const std::string& destination);
+    
     enum StandardLocation
     {
       HOME,