Add more meaningful error messages when adding users to blogs doesn't work
Please also refer to #592 (http://redmine.gc.cuny.edu/issues/show/592#change-2281) and #593 (http://redmine.gc.cuny.edu/issues/show/593).
When adding users to a common blog, the error messages don't help the user figure out what he/she is doing wrong. Errors such as user name should be all lowercase or can't have hyphens in it don't seem to be valid. Also, perhaps we should suggest how an admin can find the information that needs to be used to fill out the form. I have attached screenshot showing some misleading error messages. (In this case, I was just using Sarah's wrong email address.)
If #593 is done - work on this ticket would be unnecessary. Thanks.