libxfixes - security update

It was discovered that there was a integer overflow in libxfixes, a library
providing a client interface to the X11 XFIXES extension.

The 32 bit field rep.length was not checked for validity, which allowed an
integer overflow on 32 bit systems. A malicious server could send INT_MAX as
length which was then multiplied by the size of XRectangle. In this case the
client would not read the whole data from server, getting out of sync.

For Debian 7 Wheezy, this issue has been fixed in libxfixes version
1:5.0-4+deb7u2.

We recommend that you upgrade your libxfixes packages.