[MRELEASE-1002] Allow to release children not listing the parent

**[Romain Manni-Bucau](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=romain.manni-bucau)** opened **[MRELEASE-1002](https://issues.apache.org/jira/browse/MRELEASE-1002?redirect=false)** and commented

children not listing the parent. If the parent list children and children doesn't list the parent cause the goal is to let them be checkout directly then the child version is not handled by the mvn release plugin at all.

See MRELEA[SE-943](https://issues.apache.org/jira/browse/SE-943) for more context

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**Issue Links:**
- [MRELEASE-943](https://issues.apache.org/jira/browse/MRELEASE-943) be more tolerant with project version
(_**"blocks"**_)

Start by reading the linked MRELEASE-943 issue for context, then trace how the Maven Release Plugin handles parent and child project versions during release. The issue names no source file or test; done means allowing directly checked-out children that do not list the parent without mishandling the child version.

Written by the indexing model from the issue text.