Warn author not set when merging

By @ch3cooli on December 15, 2012 10:19 (imported from Google Code)

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What steps will reproduce the problem?

1. Do not set global and local config user
2. Open Log Dialog
3. Right click a revision -> Merge
4. click OK

What is the expected output? What do you see instead?
Actual: Merge failed
Expected: Warn author not set

What version of TortoiseGit and msysgit are you using? On
what operating system?
TortoiseGit 1.7.15

It is better to warn author not set, just like commit dialog.