[sugar] fix for 1846, sugar crashes when nick is whitespace

[Dan Williams]

On Fri, 2007-06-29 at 10:44 -0400, Owen Williams wrote:
> Here is a patch for http://dev.laptop.org/ticket/1846.  I am just
> patching intro.py to reject usernames that are all whitespace and to
> trim excess whitespace on either end.
> 
> Also, when a user supplies a blank nickname and presses the forward
> button, I briefly flash the "My Name:" label.  This can be changed if
> there's a better way to indicate why the interface is refusing to
> advance.

Looks good, Marco, can you apply?

dan