[tclwebtest] Request to add user_agent_id proc

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

This patch replaces the previously broken patch adding the feature
of changing the user agent identification from user scripts through
a defined interface.

-- 
 Grzegorz Adam Hankiewicz, gr...@ef.... Tel: +34-94-472 35 89.
 eFaber SL, Maria Diaz de Haro, 68, 2         http://www.efaber.net/
 48920 Portugalete, Bizkaia (SPAIN)