Fix bug in the modifyProperty method of ValueAnalysisState
(which is used by the MODIFY keyword of automata):
Only lower case variables could be modified,
because the full string was converted to lower case.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13273 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c