* include/libvirt/libvirt.h.in: add the networks APIs

        * include/libvirt/virterror.h: add some error codes

        * src/driver.h: add network driver vtable

        * src/hash.c: add networks hash

        * src/internal.h: add virNetwork

        * src/libvirt.c: hook up the APIs to the network
        driver

        * src/libvirt_sym.version: add the new APIs

        * src/virterror.c: handle the new error codes