Fix a performance problem in DefaultReachedSet.getPrecision():
it converted the abstract state to a string each time it was called.

Also fix the underlying problem in other cases:
String concatenation in the arguments to checkArgument() and
checkState() is bad!
Always use format strings.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13160 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c