lyp uses same scratch directory for multiple users

[kwetal]

Using Lyp 1.3.11 on Ubuntu.

$ lyp compile OnzeVader.ly 
Permission denied @ rb_sysopen - /tmp/lyp/session.1227.yml

Reason for the "permission denied": the scratch directory /tmp/lyp has been created earlier by another user on the same computer and gives only write access to that other user. All other users on the computer cannot run lyp because they do not have write access to the scratch directory.

Please use a unique scratch directory for every invocation of lyp.