Re: [HACKERS] path toward faster partition pruning

Description of the attached patches:

0001: add new tests for partition-pruning

0002: patch that makes all the changes needed in the planer (adds a stub
      function in partition.c)

0003: patch that implements the aforementioned stub (significant amount of
      code to analyze partition clauses and gin up bounding keys to
      compare with the values in PartitionBoundInfo; the actual function
      that will do the comparison is just a stub as of this patch)

0004: make some preparatory changes to partition_bound_cmp/bsearch, to be
      able to pass incomplete partition keys (aka, prefix of a multi-
      column key) for comparison with the values in PartitionBoundInfo
     (just a refactoring patch)

0005: implements the stub mentioned in 0003 and finally gets the new
      partition-pruning working (also disables constraint exclusion using
      internal partition constraints by teaching get_relation_constraints
      to not include those).

Feedback greatly welcome.