Add a variable to see the source who/what called s_doPlugins

[#1]

Since there are tons of reasons why the s_doPlugins function is called, it would be beneficial to have a parameter to read who/what called the function. Currently it's hard to write fool-proof code since a simple click somewhere on an empty space of the document already calls s_doPlugins.

[#2]

Absolutely!!!

And here's one reason why:

s.eVar2 =s.getValOnce('eVar2', s.prop2, (30/60/24));

Looks innocuous, right? 

But e.g.  a client'side form validation scenario with Form Analysis enabled, say s.prop2 is given a value and do_Plugins is called because of a click, eVar2 is assigned a value and the cookie is written, but no data is sent.

When the users submits the form and s.sendFormEvent() or s.tl() is called eVar2's value will be cleared.