Fix blender internal preview rendering continuously restarting after recent
viewport render changes.

Actually was an older issue that would cause unnecessary preview render restarts
if the render result was not allocated before it was drawn. Now the render result
is being reallocated each time for freestyle which made the issue worse.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56275 954f8c5b-7b00-dc11-b283-0030488c597c
Fix flickering black tiles in preview render, after viewport render commit, it's
nicer when the new preview draws over the old one.

The code was changed so that the render result is freed all the time because
freestyle manipulates render layers. Now it only does it when freestyle is
enabled so cycles and regular blender internal can still avoid it.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56276 954f8c5b-7b00-dc11-b283-0030488c597c
Fix cycles build error, RNA C++ API did not properly handle output parameters.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56277 954f8c5b-7b00-dc11-b283-0030488c597c