Needless character restriction in usernames.

[kfogel]

I tried to create a user named (pseudonymously here) "foo.bar", via the usual temporarily-enabled /signup route, and received this error right below the username field when I hit the "Create My Account" button:

only use letters, numbers, '-', '_'

So the user became "foobar", fine. But that's lame. Why should "." not be allowed?