improve statistics export in CPAchecker wrapper.
improve statistics export in CPAchecker wrapper.

Before: we match every substring.
After: we match only at line-starts, and we warn if there are multiple matches.

ultimate-pa/benchexec,dbeyer/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,dbeyer/benchexec,ultimate-pa/benchexec