[COMMITTERS] pgsql: Refactor merge path generation code.

Refactor merge path generation code.

This shouldn't change the set of paths that get generated in any
way, but it is preparatory work for further changes to allow a
partial path to be merge-joined witih a non-partial path to produce
a partial join path.

Dilip Kumar, with cosmetic adjustments by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/59649c3f1cbd536314c0060dcabd234deab148b2

Modified Files
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src/backend/optimizer/path/joinpath.c | 461 ++++++++++++++++++----------------
1 file changed, 250 insertions(+), 211 deletions(-)