[MRELEASE-721] Release plugin should not operate on current SVN trunk/branch to create the tag

**[Sebb](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=sebb@apache.org)** opened **[MRELEASE-721](https://issues.apache.org/jira/browse/MRELEASE-721?redirect=false)** and commented

AIUI, the release plugin currently updates the trunk (or branch) working copy in order to create the RC tag.

This is inherently unsafe, as the trunk loses its SNAPSHOT status for a short while.

Also, if the RC fails, trunk has to be reset in order to start again.

A better method would be to check out trunk into a new working copy, update that, and create the tag from the new WC.

This has the added benefit of creating a clean working copy.

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**Issue Links:**
- [MRELEASE-845](https://issues.apache.org/jira/browse/MRELEASE-845) Improvements to processing strategy

The issue identifies the release plugin's SVN trunk/branch working-copy workflow but names no files or tests. Start by tracing that workflow and reviewing the linked MRELEASE-845 processing-strategy issue; done means release-candidate tagging uses a separate clean working copy without changing the current trunk or branch.

Written by the indexing model from the issue text.