learnHash() was always called in conjunction with add_hash(). The
pattern was that a local filename and a hash were connected in
the hash-to-filename and the filename-to-hash maps. Then, the
original picture-filename or url were registered in the filename-to-hash
map.
This commit changes learnHash() to take three parameters (original-filename,
local-filename and hash) and do all of the above. The new code is
simpler because no dummy picture struct has to be generated in
DiveListView::loadImageFromURL().
The tests were extended to check for all hash<->filename associations.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
