Enable/Disable save button in the frmQuery.

Hello,

I believe that when you save a document in the form "frmQuery", the
"Save" button should be disabled to become more obvious to the user that
the document contains no changes.

When user change the document, the button is enabled again.

As with some text editors.

I know that in this case, the title appears with an asterisk, but I
think it would be better as well.

What do you think?

I have a patch for this.