Add support for Relative Paths in the Test Runner

This patch adds support for using relative paths
with the '-r' or '--relative' methods.  This can
be useful if you want to output HTML (with the
'--output-html' option) and use it in a webpage.

Additionally, the '-o' was removed from the documentation
of '--output-html', since it hasn't worked for that in a
while ('-o' means open in browser instead).