We have v1.9 and also get the '//' at the bottom of each page... and can't help much with your first question. We have wikis and users put up with the //. We are looking forward to having a go with NWiki in 2.0
To edit the help information go to Administration > Language > Language Editing and select the 'Edit help documents' link. The dropdown provides all the help files, search for the appropriate file e.g. wiki/howtowiki.html... Edit the 'Local modifications' by copying/pasting the content from one of the Master packs. Your local modifications when saved will override the master pack.
I hope this helps