Weird generic types in DefaultFixedPointSystem

[msridhar]

When fixing another bug, I noticed some strange generic type instantiations in DefaultFixedPointSystem. In particular, all the addStatement methods instantiate generic types with ? or no type parameter instead of using T, e.g.:

https://github.com/wala/WALA/blob/master/com.ibm.wala.util/src/com/ibm/wala/fixedpoint/impl/DefaultFixedPointSystem.java#L107
https://github.com/wala/WALA/blob/master/com.ibm.wala.util/src/com/ibm/wala/fixedpoint/impl/DefaultFixedPointSystem.java#L122

I was going to go through and fix these to refer to T, but then I wondered if there is some good reason for the code to be this way. @juliandolby @sjfink any idea what is going on here?