Fixes to the symbolic value solving/simplification code.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/symbolicvalue@12019 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Fixed an issue of infinite recursion.

The problem was that the algorithm to update symbolic formulas in the current state generated "new" states, even when the symbolic formulas were "equal". Added some sanity checks that prevent copying the symbolic value if it wasn't changed, also added an equals() method.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/symbolicvalue@12020 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Added debug output to track number of unique symbolic values.