Fixed two TODOs in the CFACreator regarding the single loop transformation. Single loop transformation now no longer creates an immutable CFA, but rather transforms a mutable CFA into another mutable CFA and an accompanying loop structure. This way, single loop transformation can be applied earlier, which simplifies the control flow in the CFACreator.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13049 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c