SD card and SWCAN cannot be used simultaneously

As the title says, the M2_SD_HSMCI and Single-Wire-CAN-mcp2515 libraries cannot be used simultaneously. For the fix, see this pull request. I’m making this post so that if anyone else runs into this issue, they can find my solution and hopefully to attract attention to the PR to get it merged.

@adamvoss @CollinK Can I get someone with merge permissions to take a look at that (and perhaps this PR as well while you’re at it). Also, you may want to weigh in on the implications of changing this pin, as I haven’t the foggiest why it was wrong to begin with.

As a side effect, this fixes a anomaly I noticed a few days ago which is I would expect that running an example SD sketch with no SD card inserted should produce:

MS: Cannot initialize the SD card: MS: Card not found

but it in fact produces:

MS: Cannot initialize the SD card: MS: Card is unusable, try another one