remove const from the filename in struct file, some gcc version barfs on it

src/backend/file.c

@@ -50,7 +50,7 @@ lumiera_file_destroy (LumieraFile self)
 {
   TRACE (file);
   lumiera_filedescriptor_release (self->descriptor);
-  lumiera_free ((void*)self->name);
+  lumiera_free (self->name);
   return self;
 }
 

src/backend/file.h

@@ -60,7 +60,7 @@ typedef lumiera_file* LumieraFile;
 
 struct lumiera_file_struct
 {
-  const char* name;
+  char* name;
   LumieraFiledescriptor descriptor;
 };