Force usernames to be lowercase by default.

We see a reasonable amount of support cases where the customer integrates with LDAP, and then find themselves in a situation where they have duplicate users differing only in the case.

• http://forums.atlassian.com/message.jspa?messageID=257293042

Its not a trivial task to create such a script and I don't think its something we should really be advertising through support.

It would be better if we forced the lower case option by default preventing this situation, then someone would have to explicitly turn on mixed case usernames.