Fix for compositor node preview sizes: Use the render output aspect ratio for estimating the required preview rect size instead of assuming a square, to avoid wasted space. Note that this does not work for newly added nodes until they have first been evaluated and a preview image has been generated (same behavior as before pynodes merge and associated preview changes).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55496 954f8c5b-7b00-dc11-b283-0030488c597c
Attempt to fix windows building with scons



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55497 954f8c5b-7b00-dc11-b283-0030488c597c