[tclwebtest] Request to add get form support

[Grzegorz A. H. <gr...@ef...>]

Approval request to commit the following patch. It adds form get
support and a little bit of documentation with embedded example. The
patch separates the logic from implementation during the do_request
build time using function pointers.

The behaviour of forms is a little bit changed: the submit button is
always sent, but only the selected one (first found being default),
and unchecked checkboxes aren't sent, which triggered a strange
post error in a web page of our intranet, and which seems to be
the behaviour of real life browsers.

According to my tests these slight changes shouldn't break anything
already working.

-- 
 Grzegorz Adam Hankiewicz, gr...@ef.... Tel: +34-94-472 35 89.
 eFaber SL, Maria Diaz de Haro, 68, 2         http://www.efaber.net/
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