[libvirt] [PATCH 0/9 v2] Refactor the configure.ac to reduce duplication

This is an update to https://www.redhat.com/archives/libvir-list/2012-September/msg01443.html Aside from the rebase, the main changes are all in the first patch, where I believe I addresses all Erics feedback with one exception. The exception was about the suggestion to support action-if-found, action-if-not-found, instead of the 2nd variant of macro. This is not actually possible, since the 2nd variant is not equivalent to a pair of calls to the 1st variant. To avoid flooding the list I've reduced this to just the first 9 patches. If these are approved there are another 30 patches to follow doing more conversions :-)