* allowing --single to be repeated
* adding --only so that only a specific test inside a unit can be run
* adding --skiptill useful to resume a test that crashed passed the problematic unit.
useful together with --clients 1
* adding --skipfile to use a file containing list of tests names to skip
* printing the names of the tests that are skiped by skipfile or denytags
* adding --config to add config file options from command line
