4310: Fix race condition between testing for tag and setting tag by reversing
order of operations: try to set the tag, and only test for it if there is an
error.
4310: Remove stderr redirect from git rev-list, add it to git tag.  Prefix log
output with "dispatch: ".  Tweak error message if rev-list fails.
Merge branch '4310-git-tag-race' closes #4310