Synopsis:
    $addtabkey(<nick>)

Technical:
    This function will add the specified nick into the tab key list

Practical:
    By pressing tab you can cycle through the nicks that just messaged you 
    or nicks that are on the channel. addtabkey will add the specified nick 
    to the list. 

Returns:
    Nothing


Examples:
    $addtabkey(panasync)            will add panasync to tab key list
    $addtabkey()                    won't return or do anything