Fixing URLs that include only one slash (IIS issue)

Some web servers such as IIS 8.5, modify URLs by replacing double slash to single slash. This means that PHP will get a bad URL and we will fail to proxy it.
For example when the user passes "http://www.google.com" to miniProxy, the script will actually get "http:/www.google.com".
The fix checks for this issue and if needed adds the missing slash.

For more information about this issue, see:
http://stackoverflow.com/questions/11130512/iis-modifies-double-slash-to-single-slash-in-querystring