use pool_lookup_deltalocation()
delta_create(): fix the sizeof()
initialize _hawkey.PackageDelta type
add hy_packagedelta_get_baseurl()
add hy_packagedelta_get_downloadsize()
package-py.c, packagedelta-py.c: share get_{str,num,chksum}()
add hy_packagedelta_get_chksum()