Try harder to fix travis BUILD_ALL builds.

SDL *also* requires Xinerama.h.  Use xorg-dev to pull in all the X dev
libraries.

Author: neilmoore

.travis/apt.pl

@@ -7,7 +7,7 @@
 
 retry(qw(sudo apt-get update -qq));
 
-my @common_libs = qw(libxcursor-dev);
+my @common_libs = qw(xorg-dev);
 
 if ($ENV{CXX} eq "clang++") {
     retry(qw(sudo apt-get install -qq libstdc++6-4.7-dev), @common_libs);