Fix PSTH saving issues

Builds/VisualStudio2013/open-ephys.sln

Source/Processors/Channel/Channel.cpp

Source/Processors/Channel/Channel.h

...ce/Processors/Editors/PeriStimulusTimeHistogramEditor.cpp

Source/Processors/GenericProcessor/GenericProcessor.h

Source/Processors/PSTH/PeriStimulusTimeHistogramNode.cpp

Source/Processors/PSTH/PeriStimulusTimeHistogramNode.h

Source/Processors/SpikeDetector/SpikeDetector.cpp

Source/Processors/SpikeDisplayNode/SpikeDisplayNode.cpp

Source/Processors/SpikeSorter/SpikeSorter.cpp

Source/Processors/Visualization/SpikeObject.cpp

Source/Processors/Visualization/SpikeObject.h