Issue a warning if "-r ." is used with two working directory parents. Rationale for not aborting instead: The first parent is usually more important as it is the local branch during a merge and commands like 'hg diff' and 'hg diff -r.' behave still identically (except for the warning of course). Added a test for log -r. with one and two parents.

abort: repository a not found!
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abort: error: Connection refused
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abort: repository a not found!
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abort: destination '../a' already exists
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abort: repository a not found!
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destination directory: q
abort: destination 'q' already exists