Minor changes/refactorings in the class Model.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12955 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Some comments/TODOs

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12956 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Bugfix: AssignmentToPathAllocator had problems in identifying the first occurence of a variable in a SSAMap. Added a test case.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12957 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Corrected the base case invariants check, so that it is less restrictive.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12958 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Corrected the step case invariants check, so that it is less restrictive.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12959 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
documentation, replacing 'null' with dummy-objects.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@12960 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
merge from trunk

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/bamRecursion@12961 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c