Make check in release.sh for changelog more strict
Make check in release.sh for changelog more strict

Otherwise it would find forward reference to future versions in old
changelog entries and accept them.

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