set_coordinates regression...but only on Travis+linux

[timholy]

There seems to be some problem new to the JLL-version that crops up only when running on Travis and only with Linux. I've documented this most clearly here (at the time that comment was written, the tests had a few debugging @show statements in them). See also #460. I've wrapped the offending tests in a check and thus I'd rate this as low priority. But it would be good to fix this eventually, as this leaves us with a hole in our testing when others submit PRs and we can't be sure they've run the tests locally.

My best guess is that xvfb-run is somehow not supplying an overall size to the framebuffer, and for some reason the canvas size that's specified by the Julia code is not taking effect. For reference,

$ xvfb-run --help
Usage: xvfb-run [OPTION ...] COMMAND
Run COMMAND (usually an X client) in a virtual X server environment.
Options:
-a        --auto-servernum          try to get a free server number, starting at
                                    --server-num
-e FILE   --error-file=FILE         file used to store xauth errors and Xvfb
                                    output (default: /dev/null)
-f FILE   --auth-file=FILE          file used to store auth cookie
                                    (default: ./.Xauthority)
-h        --help                    display this usage message and exit
-n NUM    --server-num=NUM          server number to use (default: 99)
-l        --listen-tcp              enable TCP port listening in the X server
-p PROTO  --xauth-protocol=PROTO    X authority protocol name to use
                                    (default: xauth command's default)
-s ARGS   --server-args=ARGS        arguments (other than server number and
                                    "-nolisten tcp") to pass to the Xvfb server
                                    (default: "-screen 0 640x480x16")

claims that it sets a finite screen size by default (640x480).