Added BLEND_COLOR, Changed TRUE and FALSE to be GLboolean

BLEND_COLOR can used as glGet parameter to get the value set with glBlendColor:
http://www.opengl.org/sdk/docs/man/xhtml/glBlendColor.xml

TRUE and FALSE are used exactly where GLboolean type is (Is*, *Mask, and others), so turning it to GLboolean makes working with these functions smooth and nice.