fix rule order so 'HAVING (X op Y)' is now parseable while 'HAVING (1+2) op Y' isn't anymore parseable... At some point we should consider more advanced parsing system than yapps.

replace get_variable_variables mecanism which can't work with some UNION queries, with get_variable_indices (eg working on selection indices instead of variable names)

* uidrels/typerels sets become uidrel/typerel, and raise error if the rql
  use multiple uid/type restriction for a variable (wasn't properly handled
  anyway, should use IN)

* blocsimplification / optrelations / attrvars set are created only when
  necessary

-> up to 5 less set per variable killed, should improve rql cache memory
   foot print and somewhat speed-up annotation