Put ioslaves on hold.
This patch couples those merged in KIO & KDEWebKit in SC 4.6.
I have to say it is probably NOT perfect and ready to merge, but I'd like to
because it is anyway a nice step over actual behavior.

It basically holds and (re)publish slave for apps needing it, letting us fixing
a long standing bug against the infamous TWO connections to do ONE thing (download, move, etc...)

It also gave me the possibility to and/or improve these things:
- better handling filenames, studying content disposition header for "attachment" and "inline" values
- better history handling, when working with kparts (also if this part needs a proper fix, IMHO reimplementing QWebHistory class...)
- a (proper?) fix for POST operations returning content. I admit I am dubious with this part and I need more testing. The nice thing
is that this patch "circumscribes" this problem, letting it easy eventually fix it again

I also copied from kdewebkit a check for exec text files mimetypes (converted to text/plain) and cleaned-up some kDebugs
(and as usual, added a lot..)

Last, sorry for the big commit message and the big/not so big patch here. It is a special case.