The patch set does not apply any more.I tried to rebase locally; even leaving out 1 ("libpq: Run pgindent after a9e9a9f32b3"), patch 4 ("Start using new libpq cancel APIs") is harder to resolve following 983ec23007b (I suppose).
Appart from that, the implementation in v19 sounds good to me, and seems worthwhile. FWIW, as said before, I also implemented it in Psycopg in a sort of an end-to-end validation.
