Validation on user signup form

[alexdobre]

Please validate the user sign up form as follows:

• username: minLength 3 , maxLength 24 characters allowed: alphanumeric, blank spaces, apostrophe ' , sedile -
• password: minLength 6, maxLength 18 characters allowed: any UTF8

Place relevant error messages on the user signup. Use non modal popus if you can to display the errors so as not to mess up the nice user layout.