Missing library.

Pretty sure these changes are correct, but Xvfb is refusing to start
under `docker build`.  Worked under `docker run`.  Investigate when
next I have time to spend on this hack.

Makefile

@@ -14,15 +14,15 @@ stage0.stamp:
 	sudo rm -rf stage0/jessie_chroot
 	touch $@
 
-stage1.stamp: stage0.stamp
+stage1.stamp: stage0.stamp stage1/Dockerfile
 	cd stage1; docker build -t xilinx:loaded .
 	touch $@
 
-stage2.stamp: stage1.stamp
+stage2.stamp: stage1.stamp stage2/Dockerfile
 	cd stage2; docker build -t xilinx:installed .
 	touch $@
 
-stage3.stamp: stage2.stamp
+stage3.stamp: stage2.stamp stage3/Dockerfile
 	cd stage3; docker build -t cryptech-alpha-builder  .
 	touch $@
 

stage2/Dockerfile

@@ -4,6 +4,7 @@ RUN ln -sf /bin/bash /bin/sh
 
 RUN apt-get update && apt-get install -y \
     libglib2.0-0 \
+    libxrandr2 \
     python-xvfbwrapper \
     ratpoison