Benchmark driver fixes#3

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siddhesh wants to merge 7 commits intovkrasnov:masterfrom

siddhesh:driver-fixes

Commits on Mar 1, 2019

Tighten up timing computation
siddhesh
committed

Commits on Mar 5, 2019

Commits on Mar 6, 2019

Allow specifying a different LuaJIT path to build the benchmark
siddhesh
committed

Commits on Mar 11, 2019