Preparation for structured types. The repodata_set_* functions now take

Preparation for structured types.  The repodata_set_* functions now take
a "handle" not an entry number.  Converting from the latter to the
former is done via repodata_get_handle.  This change required adjusting
all callers and in order to not miss any I changed all arguments from
"entry" to "handle".  That's why this is a big change.  It should be a
no-op, though (I tested this patch on top of some other changes, so
let's hope that was enough).