Search for CA bundles in places other than the one hard-coded at comp…

[keithbowes]

…ile-time.

Seemingly fixes #182, #184 and perhaps others.

[TheAssassin]

Hi, thanks for your PR. The only issue I see with this is that it applies the change only to one HTTP request more or less, but zsync2 is performing a lot more afterwards.

Could you adapt your PR to add this functionality to all the HTTP requests?

[keithbowes]

Could you adapt your PR to add this functionality to all the HTTP requests?

Probably not. I recently tried to compile it and it took a lot of work to get it even to compile. It's not so much a problem with itself but with its outdated dependencies (the problems I encountered were all fixed upstream in the respective projects but AppImageUpdate seems to require older versions of the dependencies). One thing that really concerns me is how outdated the version of libcurl used is, full of security vulnerabilities.