[Xcb] const XCBGetSetup

[Ian Osgood]

Vincent,

The recent DOxygen patch to xcb.h also changed the const-ness of  
XCBGetSetup's return value. Assuming this was intentional, I also had  
to fix xcb_conn.c to match in order to compile.  There are also lots  
of warnings introduced in xcb-util, when passing the const  
XCBConnSetupSuccessRep * to XCBConnSetup*Iter(). Should these  
prototypes also change to use a const value?

Ian