Platform: don't set swap inteval implicitly in GlfwApplication.

src/Magnum/Platform/GlfwApplication.cpp

@@ -136,7 +136,6 @@ bool GlfwApplication::tryCreateContext(const Configuration& configuration) {
     glfwSetScrollCallback(_window, staticMouseScrollEvent);
 
     glfwMakeContextCurrent(_window);
-    glfwSwapInterval(1);
 
     /* Return true if the initialization succeeds */
     return _context->tryCreate();
@@ -147,6 +146,10 @@ GlfwApplication::~GlfwApplication() {
     glfwTerminate();
 }
 
+void GlfwApplication::setSwapInterval(const Int interval) {
+    glfwSwapInterval(interval);
+}
+
 int GlfwApplication::exec() {
     while(!glfwWindowShouldClose(_window)) {
         if(_needsRedraw) {

src/Magnum/Platform/GlfwApplication.h

@@ -173,6 +173,14 @@ class GlfwApplication {
          */
         void swapBuffers() { glfwSwapBuffers(_window); }
 
+        /**
+         * @brief Set swap interval
+         *
+         * Set `0` for no VSync, `1` for enabled VSync. Some platforms support
+         * `-1` for late swap tearing. Default is driver-dependent.
+         */
+        void setSwapInterval(Int interval);
+
         /** @copydoc Sdl2Application::redraw() */
         void redraw() { _needsRedraw = true; }