src/gfxcore.cc: Don't try to close the movie if we aren't producing
one.
src/mainfrm.cc: Make right click in an empty presentation mark the
current position and open it to edit, instead of crashing.
src/guicontrol.cc,src/guicontrol.h: Rename scale/rotate lock
constants to have a "lock_" prefix.
src/mainfrm.cc: Make the Presentation->Play menu item a checkbox,
to avoid a warning with wxMSW 2.9.5.  Reported by Brian Clipstone.
src/aven.cc: Fix to build with wx 2.9.5 with wx2.8 compatibility
disabled.