Various fixes for the spec file

Various fixes for the spec file

This includes various things:
 - fix the Requires: libvirt-client to use %{name} to allow easy
   renaming
 - when building ESX support one need libcurl-devel
 - remove Makefile[.in] from xml/nwfilter in the docs, as this breaks
   parallel install ation of i686 and x86_64 packages
 - don't include nwfilter config files if not building with the daemon
all relatively trivial which is why I packed them together
* libvirt.spec.in: fix various small bugs