Here is a rebase. I made some tests use actual expressions instead of just 0 and 1. No other changes.
Sigh. Better with the attachment. Sorry for the noise.
Here is a very minor rebase.
I'm a smidge worried about this. It seems like psql is growing a scripting language. Do we want to go our own way with a kind of organically grown scripting system? Or should we be looking at embedding client-side scripting in a more structured, formal way instead? Embed a lua interpreter or something?
few scripting features doesn't mean scripting language. \if in psql is nice feature that reduce duplicate code, unreadable code, and helps with deployment and test scripts. pgbench and psql should to have similar environment - and I am thinking so \if should be there.
Using Lua is not bad idea - in psql too - I though about it much, but in this case is better to start from zero.
