Work around jrunscript bug

In certain versions of jrunscript, you cannot get a method and invoke
it... It throws a 'java.lang.UnsupportedOperationException: invocation
not supported'.

So let's play dumb, instantiate the CommandLine class, and invoke a
static method on the instance. Because that works.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>