The macro USE_LIGHT_SHADOW_COLOR actually was being defined when the shader used SHADOW (the output shadow color), not the shadow color set for the light so it's better named USE_OUTPUT_SHADOW_COLOR. In 3D there's not that difference but renaming as well for consistency.
(cherry picked from commit b69e422af9)
-=-=-=-=-=-=-=-=
-Changed material unshaded property for an enum, which supports light-only shading
-Added a "Mix" shading mode, useful for using lights as masks
-Added energy parameter to Light2D
-=-==-=-=-=-=-=-
-Small fixes in canvas item light shader
-Fixed compilation in server target
-Export for Android makes 32 bits display as default
-changed version to 1.1beta1
Added support for 2D shadow casters.
*DANGER* Shaders in CanvasItem CHANGED, if you are using shader in a
CanvasItem and pull this, you will lose them. Shaders now work through a
2D material system similar to 3D. If you don't want to lose the 2D
shader code, save the shader as a .shd, then create a material in
CanvasItem and re-assign the shader.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=
-Auto indenter in code editor, this makes it much easier to paste external code.
-Zoom in 2D viewport now uses the mouse pointer as reference.
-Obscure hack to see where code/line of GDScript in C++ backtrace.
-Fixed a bug where keys would get stuck on X11 if pressed simultaneously
-Added Api on IP singleton to request local IPs.
-Premultiplied alpha support when importing texture, editing PNGs and as a blend mode.
