[libvirt] [PATCH] Add virConnectGetLibvirtVersion API

Hi all, The attached patch adds a new API call for retrieving the libvirt version used by a connection: virConnectGetLibvirtVersion. Without this, there is currently no way to determine the libvirt version of a remote qemu connection for example. This info can be useful for feature detection/enabling/disabling. As an example, virt-install may want to use the AC97 sound device as the default sound model for new VMs. However, this was only added to libvirt's white list in 0.6.0, while the other models have been available since 0.4.3. If installing a remote guest, virt-install will want to ensure that the remote libvirtd is >= 0.6.0. Granted, the remote version could have backported the AC97 patch and virt-install would be incorrect, but better to be overly restrictive than to blindly specify AC97 and have guest creation bomb out. The 'correct' way to handle the above issue would be some combination of dropping internal whitelists from libvirt and generating them from info reported by the hypervisor, and advertising the available values in the capabilities XML. However I think this API addition makes things more manageable with little downside until a proper solution is implemented. Thanks, Cole