nvs_flash: Version compatibility check for nvs storage

This change adds a check for compatibility between the nvs version
found on nvs flash and the one assumed by running code during nvs
initialization. Any mismatch is reported to the user using new error
code ESP_ERR_NVS_NEW_VERSION_FOUND.

examples/protocols/esp_http_client/main/esp_http_client_example.c

@@ -351,7 +351,7 @@ static void http_test_task(void *pvParameters)
 void app_main()
 {
     esp_err_t ret = nvs_flash_init();
-    if (ret == ESP_ERR_NVS_NO_FREE_PAGES) {
+    if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
       ESP_ERROR_CHECK(nvs_flash_erase());
       ret = nvs_flash_init();
     }