back-stamped for this.

large planning problems: when the list of join rels gets too long, make
an auxiliary hash table that hashes on the identifying Bitmapset.

should have been caught by the src/tools/copyright script ... why
weren't they?

make sure the $Id tags are converted to $PostgreSQL as well ...

node emits only those vars that are actually needed above it in the
plan tree.  (There were comments in the code suggesting that this was
done at some point in the dim past, but for a long time we have just
made join nodes emit everything that either input emitted.)  Aside from
being marginally more efficient, this fixes the problem noted by Peter
Eisentraut where a join above an IN-implemented-as-join might fail,
because the subplan targetlist constructed in the latter case didn't
meet the expectation of including everything.
Along the way, fix some places that were O(N^2) in the targetlist
length.  This is not all the trouble spots for wide queries by any
means, but it's a step forward.

Instead of Lists of integers, we now store variable-length bitmap sets.
This should be faster as well as less error-prone.