C-u C-x = prints garbage for a text property with value '(string . ?")

[Alan Mackenzie]

Hello, Emacs.

In master (probably in emacs-25, too), give a character a text property
with value (string . ?").  When `describe-property-list' (descr-text.el)
comes to print it, it decides that (string . ?") is a "widget" (whatever
that is), and instead of printing the actual value, it ignores the cdr
and prints the car as follows:

    string (widget)Top

It decides that 'string is a "widget" because the symbol string has a
widget-type property.

This is crazy!  If somebody does C-u C-x = to see the value of the text
properties, surely that is what she should see?  Not some "look how
clever I am" DWIM attempt that only prints half of the value?

I don't see the logic in this handling, therefore don't feel qualified
to fix this bug.  Would somebody help me out, please.

-- 
Alan Mackenzie (Nuremberg, Germany).