Fix for #85 client returns bad channel names for fetch of zero-length span or full-gap span

This is due to a difference between nds1 & nds2 channel listing. NDS1 includes s-trend/m-trend in the channel name when doing listings and NDS2 does not. Reading buffers from frames returns channel names w/o m/s-trend.

Make the gap handler return names that match the buffer instead of the nds1 channel list (strip out m/s-trend). No data is lost, the type is still present in the Type() method.