If the user keeps one finger down they can still generate new right click events
Previously in multitouch events, we supported only one right click event starting from one finger down.
The user subsequently had to restart the multitouch mode for another right click; hence lift all fingers
from the surface and start again.
New behavior allows user to generate a new right click while holding one finger down and putting down and lifting a second finger.
I think this is more intuitive and user friendly, although it might require some getting used to, if one was accustomed to the old behavior
supportedGraphicsModes() now returns to OSystem_SDL a pointer to a deep copy of
surfacesdl's internal graphics mode array. Therefore each can free its
own copy without interfering with the other's.
If a game and graphics mode were chosen from the command line, the normal
plugin might not have been loaded and it would crash upon being used to
scale the cursor. Now the normal plugin is initialized with the first
plugin to be initialized.
oldSrcScale() is now unified with scale(). Use enableSource(bool enable)
to switch functionality. Partial screen updates are also posible because
of this.
initialize() had its prototype changes although it is functionally the
same.
setSource() no longer has a type parameter, removing support for
multiple source surfaces. They weren't useful anyway.
useOldSrc() was renamed to useOldSource() to conform to the names of
other functions.
More bookkeeping is kept in common scaler code instead of the backend.
Plugins inheriting SourceScaler will have this functionality.
TODO: Some new functions may still be able to be combined to simplify
the API.
If the two source images match, the scaler assumes there is not update
and does not draw to the surface. However, AR correction depends on a
redraw, so the scaler always writes to _destbuffer which is then copied
to _hwscreen to be AR corrected.
