[twill] 'formfill' extension module

[Titus Brown]

Hi all,

motivated by some mailman adventures & a discussion with Ben Bangert,
I've added a 'formfill' extension module.  Docs here:

http://issola.caltech.edu/~t/twill/doc/extensions.html#formfill-convenience-functions-for-filling-out-forms

This extension module adds three new functions:

   fv_match <form> test-(\d+) 'hello world!'

   fv_multi <form> field1=value1 field2=value2 ...

'fv_multi_sub' does the same thing as 'fv_multi' and then executes
'submit'.

(Thanks to Ben Bangert for the idea!)

--titus