[Development] Updating the minimal supported version of libxcb

[Александр Волков]

Hi,

Currently Qt supports libxcb 1.5, which is very old (it was released on 
December 3, 2009)
It complicates adding new bundled xcb libraries, because they have to be 
checked
for compatibility with this old version and maybe patched.

Qt officially supports the following platforms that use libxcb:
OpenSuSE 13.1 (libxcb 1.9.1, xcb-proto 1.8)
Red Hat Enterprise Linux 6.6 (libxcb 1.9, xcb-proto 1.8)
Ubuntu 14.04 - 64bit (libxcb 1.10, xcb-proto 1.10)

What do you think about updating the minimal supported version of libxcb 
to 1.9?

Regards,
Alexander