awful.tag: add index property for custom tag order

Signed-off-by: Uli Schlachter <psychon@znc.in>
Send correct size to fullscreen clients (FS#1093)

Titlebars are not visible for fullscreen clients, so it doesn't make sense to
substract the area used for the titlebar in ConfigureNotify events.

Signed-off-by: Uli Schlachter <psychon@znc.in>