This should happen together with other taint types. We should simply pay attention if the incoming taint is numkey, to see which keys it can be propagated to. Might also want to ensure that the logic for setting NUMKEY on keys in Taintedness is up-to-date, as we're going to use that for unknown keys. Future (?) TODO might be to have a separated property for int vs non-int unknown keys. Aside from the improved accuracy, there's also a bunch of legacy code that we can remove once this is done:

• Temporary parameter to markAllDependentMethodsExecForNode, conditional in backpropagateArgTaint; possibly merge the two
• getObjsForNodeForNumkeyBackprop
• SECCHECK_NUMKEY_SPERIMENTAL env variable
• separate category of "numkey" tests (can be just merged back into the normal integration category)