Index-only scans for GIST

Hi, hackers!
I work on a GSoC project "Index-only scans for GIST"
https://wiki.postgresql.org/wiki/Support_for_Index-only_scans_for_GIST_GSoC_2014

Repository is
https://github.com/lubennikovaav/postgres/tree/indexonlygist2
Patch is in attachments.

It includes index-only scans for multicolumn GIST and new regression test.
Fetch() method is realized for box and point opclasses.

Documentation is not updated yet, but I'm going to do it till the end of
GSoC.

I've got one question about query with OR condition. It is the last query
in regression test "gist_indexonly". It doesn't fail but it doensn't use
index-only scans. Could someone explain to me how it works?
It seems to depend on build_paths_for_OR
<http://doxygen.postgresql.org/indxpath_8c.html#ae660d2e886355e53ed3b9ec693e4afd2>
function.
But I couldn't understand how.

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Best regards,
Lubennikova Anastasia