[Libguestfs] [PATCH nbdkit v2 0/9] curl: Use curl multi interface

This is a slightly cleaner version of the patch previously posted here: https://listman.redhat.com/archives/libguestfs/2023-July/032167.html Patch #8 is still irreducibly complex, but I can't see an easy way around that. I spent more time refining the commands that get passed to the worker thread so that now there are only two (EASY_HANDLE and STOP), since all operations can be expressed in terms of just those two commands. Test & valgrind all pass, and there are no missing features. Rich.