hh_single doesn't need hhi files

Summary: Set this for unit tests so we don't need the hhi archive lying
around, since we don't use it anyways -- but the `Naming` error case
might still try to read it.

Reviewed By: @elgenie

Differential Revision: D1422029
Add touching hhi files to the heater

Summary: Some systems are pretty aggro about cleaning up `/tmp`, so
let's keep poking the mtime of these files as long as we're using them.

Reviewed By: joelb, eletuchy

Differential Revision: D1423210
Clean up uses of Type::unbox() in MInstrTranslator

Summary: We were assuming that the result of a LdRef instruction would always
be typeParam.unbox(), but this isn't the case. I went through all the uses in
minstrtranslator and audited each one, either commenting on why it's ok or
fixing it to use ldRefReturn. The call to checkMIState() is now after
emitBaseOp() because none of the base ops actually needed it and this allows us
to use m_base in checkMIState() instead of duplicating some of its logic.

Reviewed By: @jdelong

Differential Revision: D1410177