Improved the exactness of fuzzy image drop search.

Some images which were present in DB and outside had only similarity of 98,13 % though they were identical.
The problem seems to be that QImage does some transformations which reduce the exactness.
Now the dropped external image is loaded as DImg which increases the similarity of the specific pictures to 99,41 %.
This is still not perfect but far more precise.

BUGS: 375142
FIXED-IN: 5.5.0