Blender Internal Render in viewport

Because of our release soon, feature has been added behind the Debug Menu.
CTRL+ALT+D and set it to -1. Or commandline --debug-value -1.

When debug set to -1, you can put the viewport to 'render' mode, just like
for Cycles. Notes for testers: (and please no bugs in tracker for this :)

- It renders without AA, MBlur, Panorama, Sequence, Composite
- Only active render layer gets rendered. Select another layer will re-render.
- But yes: it works for FreeStyle renders!
- Also does great for local view.
- BI is not well suited for incremental renders on view changes. This only
  works for non-raytrace scenes, or zoom in ortho or camera mode, or for 
  Material changes. In most cases a full re-render is being done.
- ESC works to stop the preview render.
- Borders render as well. (CTRL+B)
- Force a refresh with arrow key left/right. A lot of settings don't trigger
  re-render yet.

Tech notes:

- FreeStyle is adding a lot of temp objects/meshes in the Main database. This
caused DepsGraph to trigger changes (and redraws). I've prepended the names
for these temp objects with char number 27 (ESC), and made these names be
ignored for tag update checking.

- Fixed some bugs that were noticable with such excessive re-renders, like 
  for opening file window, quit during renders.




git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56099 954f8c5b-7b00-dc11-b283-0030488c597c