[Libguestfs] [PATCH 0/4] lib: qemu: Memoize qemu feature detection.

Doing qemu feature detection in the direct backend takes ~100ms because we need to run `qemu -help' and `qemu -devices ?', and each of those interacts with glibc's very slow link loader. Fixing the link loader is really hard. Instead memoize the output of those two commands. This patch series first separates all the code dealing with qemu into a separate module (src/qemu.c) and formalizes the interface to this module. Then I had to rearrange the code we use to create /var/tmp/.guestfs-<UID> for the supermin appliance to src/tmpdirs.c. The final patch adds the memoization, storing this in the supermin appliance cache directory. Rich.