The standalone build does not bundle its own ssh, so should be built
to support as wide an array of ssh versions as possible, so turn off
connection caching.
Unfortunatly, as implemented this forces a full rebuild when building the
standalone binary, and of course it makes it somewhat slower.
This is not ideal, but neither is probing the ssh version every time it's
run (slow), or once when initializing a repo (fragile).
3156febec8