Added a bunch of things from X11 headers needed for implementing clipboard interfacing

[aweinstock314]

No description provided.

[jdm]

r? @metajack

[aweinstock314]

This is failing to build on travis due to the dependency Xmu ("/usr/lib/x86_64-linux-gnu/libXmu.a" on the Debian system I'm using for development) not being found. Xmu contains the symbol _XA_CLIPBOARD (declared extern in "/usr/include/X11/Xmu/Atoms.h"), which is an X11 Atom (interned string) used as part of the protocol(s) involving the clipboard. How do I go about adding Xmu to the relevant dependencies list (assuming that's the correct way to go about resolving this)?

[Manishearth]

Add an install key:

install:
 - sudo apt-get install foobar

You will have to remove the sudo: false from the top, sadly

[metajack]

This will prevent it from using containerized builds, which means it will be slower to go through CI. If we can avoid an apt-get dep we should, but if we can't, we'll just have to live with the degraded performance.

[jdm]

I assume we want libxmu6-dev, not just libxmu6?