DIB Engine - Mostly fixed against test suite

[Massimo Del Fedele]

Well, it seems that the engine fixes some unrelated bugs too :-)
Bugs 15146 and 10408, as reported by a tester.

BTW In a couple of weeks all (few) remaining failing tests should be fixed.
Then I'll try to optimize somehow the mixed blitting, which is the only
stuff that remains slower than original.

Then, last but not least, I guess I'll setup a machine for weekly packaging
for ubuntu.... many people are asking me for autocad usage.

Ciao

Max