[Libguestfs] [PATCH nbdkit 0/9] Generic vector, and pass $nbdkit_stdio_safe to shell scripts.

This was a rather longer trip around the houses than I anticipated! The basic purpose of the patch series is to set $nbdkit_stdio_safe to "0" or "1" in sh and eval plugin scripts. To do that, I ended up adding a nicer way to manipulate environ lists, and to do that, I ended up adding a whole generic vector implementation which is applicable in a lot of different places. Rich.