Maps repository users to Redmine users (#1383).

Users with same username or email are automatically mapped. Mapping can be manually adjusted in repository settings. Multiple usernames can be mapped to the same Redmine user.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2006 e93f8b46-1217-0410-a6f0-8f06a7374b81