Removed excess assertion check from PointerTargetSetManager; fixed a bug

 -- merges of same bases with different types can really occur (e.g.
    test/programs/simple/merge-bases-union_true-unreach-label.c)

 -- fixed a bug in DeferredAllocationPool (PersistentList merging) incroduced during the refactoring in 10058
    (the negation was lost)

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14629 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c