composer/composer — pull request #3580 by Pherserk (2014-12-21 11:43:48+00:00)
Title: Delegate problem message formatting to a dedicated class

Exception was tought to know the installed map, now installed map is a dependency of the problem formatter.
More than one potential failure cause can be noticed now.
Sorry, surely it needs some evolution or refactoring, just a little step over the goal.