render input id correctly if it is changed

[jimgregory]

It's sometimes necessary to change a form element's ID after it's been created (e.g., when there are multiple form elements with the same name). A bug existed that prevented the ID in the input widget from updating:

In [1]: from web import form

In [2]: f = form.Form(form.Textbox('x'))

In [3]: f.render()
Out[3]: u'<table>\n    <tr><th><label for="x">x</label></th><td><input type="text" id="x" name="x"/></td></tr>\n</table>'

In [4]: f.x.id = 'newx'

In [5]: f.render()
Out[5]: u'<table>\n    <tr><th><label for="newx">x</label></th><td><input type="text" id="x" name="x"/></td></tr>\n</table>'

Note the label's ID has been updated but not the input's ID. This fixes that bug.

[jzellman]

🚢