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.
=======================
Should display 'First commit message'
description:
First commit message
=======================
Should display 'Second commit message'
description:
Second commit message
=======================
Should display 'Third commit message\n This is the 3rd log message'
description:
Third commit message
This is the 3rd log message
=======================
Should display 'Fifth commit message\n This is the 5th log message'
description:
Fifth commit message