[FR] Safe figure saving

[isentropic]

Perhaps savefig should be safe by default and error upon already existing file, and have a unsafe tag. This has hurt me multiple with multiple libraries. In scientific context it is better not to override by default I think. This is breaking, but it should be better long term.

[t-bltg]

I'm skeptical about this. I believe this should be the other way around (if ever implemented), savefig with an optional safe=false keyword, defaulting to overwriting the files.

[isentropic]

Maybe we can reopen this @t-bltg ? Unsafe saving has burned all of us at some point. Maybe we discuss this with the community>

[oameye]

I am with @isentropic on this one.