Default suite name changed from numbers to case name (patch/pr-5)

The default suite name is used when a test case file (rather than suite file) is given on the selenese-runner command-line. 

When selenese-runner is invoked multiple times with different case files this results in the suite name being 0 for all cases which makes it impossible to use the same result-directory for all cases as previous results are overwritten.

Please review possible side-effects before merging.