If develop or master can't be found, existing branches should be listed

[asbjornu]

When BranchConfigurationCalculator.InheritBranchConfiguration() can't find a develop or master, it would be very useful for debugging purposes (as I found in #912 (comment)) if the branches it does find were joined together in the exception message.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. After 30 days from now, it will be closed if no further activity occurs. Thank you for your contributions.