Bump version number to current 1.1.5
Add missing URL attribute to setup.py
Add libvirt version check macro from libvirt upstream

Add LIBVIRT_CHECK_VERSION from libvirt upstream so that we can check the
version of the library we are compiling against and support a range of
libvirt versions. The macro was added to libvirt in 1.1.5 so we must
provide it if its not defined.