Don't move clients on ConfigureRequests (FS#1030)

I never saw a single program that set a border on its own windows. However,
awesome commonly sets borders on its clients and the position of a client is the
part outside of the border. So when processing a position request from a client,
we also have to include this border and fix things up correspondingly.

However, the same isn't needed for the client size, because the size does not
include the borders, but just the titlebar plus the "real" client content.

Thanks to Daniel Hahler for providing a simple test case based on urxvt for
debugging this!

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