lib/param: handle (ignore) substitution variable in smb.conf

[github at samba.org]

New comment by rodo on Samba Github repository

https://github.com/samba-team/samba/pull/12#issuecomment-147674166
Comment:
Thanks for this patch @QGuLL I have exactly the same problem and do monkey patch each time a new version is released and deployed on our infra.
Hope to see it merge soon, as I see on https://bugzilla.samba.org/show_bug.cgi?id=10722 there is no technical issues to see it in next release, or in next hotfix.