Hierarchical queries a la Oracle patch. for 7.3rc1.

Hi there!

This is a new version of patch i've posted.
It's applied to version 7.3rc1.

Changed syntax, now it's more closer to Oracle's and allows operator other
than '='.
Removed Const/Var trick, now it's a new FakeVar node used, as a side effect
it's not need initdb now.
Added little regression test.
Added more comments on code.
A bit extended README.hier .

regards,

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.evgen