Merge branch 'master' into viewport

# Conflicts:
#	examples/imgui_impl_opengl3.cpp
#	imgui.cpp
#	imgui.h
#	imgui_draw.cpp
#	imgui_internal.h

examples/example_glfw_opengl2/main.cpp

@@ -24,6 +24,8 @@ int main(int, char**)
     if (!glfwInit())
         return 1;
     GLFWwindow* window = glfwCreateWindow(1280, 720, "ImGui GLFW+OpenGL2 example", NULL, NULL);
+    if (window == NULL)
+        return 1;
     glfwMakeContextCurrent(window);
     glfwSwapInterval(1); // Enable vsync