Now you can have your current directory anywhere and call
runtests.sh with full path and it'll find the way to
nosetests and the tests directory on its own.
Most useful if you're inside the mediagoblin/ dir and can
just call "../runtests.sh".
If you don't give an option argument (starting with a dash)
to runtests.sh then it will append the directory with all
the tests to the commandline of nosetests. That way it will
only search there for tests.
If nose isn't installed, then runtests.sh says it can't find nosetests
and exits, but doesn't tell you what you need to do to fix the situation.
This fixes that.
