OR clause indexing installed

I have installed my changes to allow use of indexes with OR clauses. It
is not perfect, but passes the regression tests. It is certainly ready
for people to try it out.

90% of the code was already there, but disabled because it was broken.
Cleanup, debugging, and some additional code was all that was needed.
I am thinking of doing a code review of the entire optimizer to make
sure the code is in good shape.

It is amazing how many PostgreSQL features are like this.

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Bruce Momjian | 830 Blythe Avenue
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