[redland-dev] New function rasqal_query_execute2()

[Victor Porton]

I implemented new function rasqal_query_execute2() and deprecated
rasqal_query_execute() and a few other functions which deals with data
graphs "attache" to a query.
rasqal_query_dataset_contains_named_graph() also should change its API.

The new function takes data_graphs argument which is currently a
sequence of data graphs. The query is applied to this set of data
graphs. This allows to apply the same query (several times) to
different data graphs without query recompilation.

The code is not yet tested (we need to create the tests).

The reason I release this preliminary code is to discuss the following:

Should the new functions take raptor_sequence* (as my code currently
does) or should we instead introduce a new "data_graphs_set" type
(instead of a sequence) specifically to hold a set of data graphs?

Please discuss this question.

Also note that my code works only with version 3 of
rasqal_triples_source structure.

My code is accessible at
https://github.com/vporton/rasqal
fork of the rasqal repository.