reworked web search

I have completely reworked the web search functionality in the core of
the browser. The new API is much simpler and robust. Currently only
two frontends (GTK and Amiga) use the functionality but I hope now
that it is so much simpler to use other maintainers might implement it
for their frontends.

I have fixed up both GTK and Amiga usage (apologies to chrisy if I
made an error in amiga) and the GTK frontend "search from the url bar"
functionality now actually works (set in preferences)

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Regards Vincent
http://www.kyllikki.org/