I think I've resolved most of my problems, this post is mostly for posterity's sake... I'm not creating bug reports because I haven't reproduced any of this and I'm not sure how machine-specific it may be. (But if anyone thinks a specific problem below should be created as a bug just let me know and I'll do that.) I'm also not really sure which steps fixed the problem, I pretty much just tried everything I came across. Also, the notes below are in no particular order.
I downloaded and unpacked df 0.31.14 as well as the Phoebus tileset package (the one for 0.31.13, I think.) I was doing this all through x2go client, a special kind of remote X Windows session. Also, Ubuntu is running as a VMWare virtual machine.
When I ran ./df from a terminal window I got two errors that appeared in pop-ups: "Dynamically opening the OpenAL library failed, disabling sound" - "SDL Initialization has Failed: Couldn't find matching GLX visual"
I installed the following packages with dependencies via aptitude:
libsdl-image1.2
nvidia-settings
nvidia-glx-173
libsdl1.2-dev
libsdl-ttf2.0-0
For safety's sake I also downloaded the latest version of SDL from
http://www.libsdl.org/release/SDL-1.2.14.tar.gzand ran configure, make, sudo make install.
I added the following sections to /etc/X11/xorg.conf:
Section "Module"
Load "glx"
Load "dri"
Load "dri2"
EndSection
Section "Extensions"
Option "Composite" "Enable"
EndSection
In the end I still get all the same errors but df opens and runs (with the Phoebus tileset enabled.) In addition to the pop-up errors listed above there are several copies of two other errors appearing at the terminal: 'xlib: extension "Generic Event Extension" missing on display ":50.0".' and "GPU does not support non-power-of-two textures, using 512x512 catalog. Resetting textures" The first error also appears in /var/log/apt/term.log.