Fix to multisearch with the new search directions

I forgot to modify Gdip_MultiLockedBitsSearch() to handle the new search
directions correctly. The current ugly workaround works correctly and
should be faster than a bunch of if-statements inside the while-loops.
Fix some returned values and add a few remarks

The OutputCount parameter has been removed from Gdip_ImageSearch(): this
value is now returned by the function (or a negative value in case of
error).