Handle multiarch libgl-mesa-dev on Ubuntu 12.04

Ideally we would be able to sudo apt-get install
libgl1-mesa-dev:amd64 libgl1-mesa-dev:i386.  Unfortunately,
these packages conflict due to a bug:
https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/949606

Instead we install the 64bit headers and binaries but only the
32bit binaries (and create a symlink to enable them).

Change-Id: I87b55533d00a82807739a5b0eb3dd7558b7e3d6c
diff --git a/src/source/initializing.md b/src/source/initializing.md
index bbe3357..82dc8c0 100644
--- a/src/source/initializing.md
+++ b/src/source/initializing.md
@@ -113,9 +113,11 @@
 
     $ sudo apt-get install git-core gnupg flex bison gperf build-essential \
       zip curl libc6-dev libncurses5-dev:i386 x11proto-core-dev \
-      libx11-dev:i386 libreadline6-dev:i386 libgl1-mesa-dev:i386 \
-      g++-multilib mingw32 openjdk-6-jdk tofrodos python-markdown \
-      libxml2-utils xsltproc zlib1g-dev:i386 libxext-dev:i386
+      libx11-dev:i386 libreadline6-dev:i386 libgl1-mesa-glx:i386 \
+      libgl1-mesa-dev g++-multilib mingw32 openjdk-6-jdk tofrodos \
+      python-markdown libxml2-utils xsltproc zlib1g-dev:i386 \
+      libxext-dev:i386
+    $ sudo ln -s /usr/lib/i386-linux-gnu/mesa/libGL.so.1 /usr/lib/i386-linux-gnu/libGL.so
 
 ## Configuring USB Access ##