Tools: make script dir optional, default to experiment id

mkexp

@@ -431,12 +431,15 @@ def list1(x, keep_empty=False):
     return [x]
 
 # Create directory for scripts if it doesn't exist
-script_dir = config['SCRIPT_DIR']
+script_dir = config.get('SCRIPT_DIR', config.experiment_id)
 print(f"Script directory: '{script_dir}'")
 time_stamp = strftime("%Y%m%d%H%M%S")
 backup_dir = os.path.join(script_dir, 'backup', time_stamp)
-if not os.path.isdir(script_dir):
+if not os.path.lexists(script_dir):
     os.makedirs(script_dir)
+elif not os.path.isdir(script_dir):
+    feedback.die("cannot create script directory"
+        f", blocked by non-directory '{script_dir}'")
 else:
     feedback.info("script directory already exists, moving existing scripts to backup")
     if not os.path.isdir(backup_dir):