BF: fix problem with trialList creation

By referring to the local variable trialList rather than the property
self.trialList, the imported list of trials was being discarded and
replaced by just the name of the conditions file. This caused
loops to fail later on when trying to access properties of a given trial.
Merge pull request #661 from m-macaskill/patch-1

BF: fix problem with trialList creation