Enable Correlated OT for Yao

[jackdoerner]

I noticed a while back that, although correlated OT code exists, YGC doesn't actually use it (nor does anything else). I have a candidate implementation here (note that it's a descendant of my currently unmerged OT splitting branch), which passes the ORAM test suite from ACK (both with and without the new YAO_DISABLE_CORRELATED_OT flag enabled). I can confirm that less communication happens when COT is enabled. There's a lot going on in the OT implementation though, and I've made some fairly significant interface changes, so I expect some discussion will be necessary.