What steps will reproduce the problem?
1. Create a form panel with:
<form:AdapterField fieldLabel="...">
    <button:Button text="Form Button" />
</form:AdapterField>

What is the expected output? What do you see instead?
The button should be wrapped in an AdapterField and displayed in the form.  
Instead, UiBinder crashes with the error "[ERROR] [client] - Found unexpected 
child element Element <button:Button text='Form Button'> (:40)".

What version of the product are you using? On what operating system?
gxt-uibinder 0.6
Internet Explorer 8
Windows 7

Please provide any additional information below.
Alternatively any non-field element included in a FormLayout could 
automagically be wrapped in an AdapterField with attributes such as fieldLabel 
being passed through to the AdapterField.  This would be nice and produce 
cleaner XML files, but it could also be confusing as it would obfuscate the GXT 
spec that says only Field subclasses are displayed in a FormLayout.