should pipeline be more flexible about how source space spacing is specified?

[drammock]

in #1045 (comment) I noticed that a source space in a dataset I had was called ...oct-6-src.fif whereas the pipeline was expecting ...oct6-src.fif (note the lack of - between oct and 6). Do either @hoechenberger or @larsoner know whether oct-6 (with the dash) is common enough in the wild to be worth checking for / using if found? Computing source spaces isn't a super long process, but for a large dataset it could add significant time to recreate them all unnecessarily.

[larsoner]

IIRC oct-6 is an older convention and we've been using oct6 for a while. But I'm fine with being flexible where if oct-6 already exists we could use it (but still always write oct6 if we compute it). Should only require a couple of lines so pretty low maintenance burden