test_rdir: only catch exceptions I raise
test_rdir: relative path tests (incomplete)

TODO: add long listing (ls -l) tests
rplot: bugfix batch mode check
rplot: configurable alpha step
rplot: helper to convert from flat list
rplot: allow for empty plots
rplot: arbitrary function to process plottable
rplot: change default styles, and off by default
rplot: allow naming canvas
rplot: support individual drawing options