Inefficient importers that convert to .bst files might be incompatible with Import MEG/EEG function

[mpompolas]

Check:
Forum discussion

I don't have more raw files from other acquisition systems, so I only check it on the invasive neurophysiology importers I wrote (in_data_plx and in_data_intan - PR #516), but I expect this to generalize to the rest of the importers that first convert the datasets to a .bst file.

[ftadel]

Fixed: 23341c5