Improve ConvFuns detection

[felixhekhorn]

closes #386

[felixhekhorn]

nono I broke something (which I had not time to investigate yet ... that I will need to do locally instead of online 😇 )

[felixhekhorn]

I wanted to deal with both "special characters" + and = at the same time, but it wasn't so trivial as I thought - so I fix only the actual problem, which is the +

[Radonirinaunimi]

I wanted to deal with both "special characters" + and = at the same time, but it wasn't so trivial as I thought - so I fix only the actual problem, which is the +

What exactly do you mean? That you cannot simply use rsplit_once also with =?

[felixhekhorn]

What exactly do you mean? That you cannot simply use rsplit_once also with =?

that was my (naive) idea, but it resulted in the error you can see above - and then I decided to do the minimal step rather then debugging

[cschwan]

While using str::rsplit_once is a straightforward solution, it's better to use str::strip_suffix and explicitly check against the cases +p, +f, +pf and +fp that we support. This allows to use + characters even in unpolarized PDF names.

If the tests all succeed, we can merge this.