On some machines (*cough* Mingw *cough*) installs are very slow. We've
ameliorated this by allowing temp installs to be reused, but the
pg_upgrade Makefile never got the message. Here's a patch that does
that. I'd like to backpatch it, at least to 9.5 where we switched the
pg_upgrade location. The risk seems appropriately low and it only
affects our test regime.
cheers
andrew
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Andrew Dunstan https://www.2ndQuadrant.com
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