Add simple binary testcase bisection script

[kripken]

This just bisects on the binary in order to find where the behavior changes. This is useful on our fuzzer as the input is additive, so just by shrinking it we get a subset of the final wasm. Full details in the source file.

I used this when I ran into

https://chromiumdash.appspot.com/commit/3295097575e8b4fd4aa46018e03ac4f669130dc4

which let me see that the diff contained ref.eq.