Add ro_mouse module to process mouse events during drags and on null polls.
Implement support in ro_mouse for tracking the mouse during drags and passing on DragEnd events.
Remove ro_gui_drag_end() and update all of its clients so that they use ro_mouse.
Remove the unused ro_gui_window_frame_resize_end().
Termination of save drags with Escape is unimplemented, but appears broken anyway.
The use of gui_drag_type is still required to handle Message_DatasaveAck processing.
Mouse tracking is still handled via gui.c.
NetSurf includes are now done with ""s and other system includes with <>s as C intended.
The scandeps tool has been updated to only look for ""ed includes, and to verify that the
files exist in the tree before adding them to the dependency lines. The depend rule has
therefore been augmented to make sure the autogenerated files are built before it is run.
This is untested under self-hosted RISC OS builds. All else tested and works.
svn path=/trunk/netsurf/; revision=3307
