Added GLFW error strings to test programs, various tweaks.

tests/defaults.c

@@ -71,7 +71,7 @@ int main(void)
 
     if (!glfwInit())
     {
-        fprintf(stderr, "Failed to initialize GLFW\n");
+        fprintf(stderr, "Failed to initialize GLFW: %s\n", glfwErrorString(glfwGetError()));
         exit(1);
     }
 
@@ -80,7 +80,7 @@ int main(void)
     {
         glfwTerminate();
 
-        fprintf(stderr, "Failed to open GLFW default window\n");
+        fprintf(stderr, "Failed to open GLFW window: %s\n", glfwErrorString(glfwGetError()));
         exit(1);
     }