parallel downloads of multiple debuginfo files

[Frank Ch. Eigler]

Hi -

> one more debuginfod question: Would it be possible to extend the API
> to allow downloading of multiple debug info files in parallel?  The
> `debuginfod_find_*` API currently only supports looking at multiple
> server urls in parallel. I would like to ask multiple files in
> parallel.

Spin up N threads, do one set of debuginfod_begin/_find/_end ops in each.
Bob is your uncle!

- FChE