start fixing the tracking of var-env

examples/DuncanExample.java

examples/SimpleArrayExprs.java

examples/XField.java

src/Javawlp/API.hs

src/Javawlp/Engine/HelperFunctions.hs

src/Javawlp/Engine/Substitute.hs

src/Javawlp/Engine/WLP.hs

src/Javawlp/SimpleFormulaChecker.hs