Duplicate stepnames in workflow.csv do not throw errors

[mmterpstra]

This should give an error and should not print the generated script of the second step over the first step.

example:

step,protocol,dependencies
Hellow,protocols/HelloWorld.sh,
SomeStep,protocols/SomeStep.sh,
Hellow,protocols/HelloWorld.sh,SomeStep;input=someStepOut;

generates:

/rundir/SomeStep_0.sh
/rundir/Hellow_0.sh

submits

Hellow_0.sh
SomeStep_0.sh
Hellow_0.sh

Crashing on the first Hellow_0.sh because this needs output of SomeStep

maybe related to #44 & #264