devel/release-checks.sh: version string problem does not halt execution
Version string has strict format requirements in release-check.sh:
only numbers and periods (in sane order) are accepted.
Mismatch there used to halt further execution.
In this case, checking versions like '*~rc1' for (more) problems
was not possible.
This 'fatal error' is now changed buffered error message like in
following tests, and is displayed at the end of execution.