Undo thinko in commit e78d1d6d4.

Silence complaints about leaks in PlanCacheComputeResultDesc.

Avoid leakage of zero-length arrays in partition_bounds_copy().

Fix MemoryContextAllocAligned's interaction with Valgrind.

Fix assorted pretty-trivial memory leaks in the backend.

Improve hash join's handling of tuples with null join keys.