Fix MassStorageKeyboard demo USE_INTERNAL_SERIAL check being performed before the required library headers were included, causing a compilation error.

Added notes to the class driver functions indicating which functions require what Device/Host state machine states to function.

Demos/Device/ClassDriver/MassStorageKeyboard/Descriptors.c

@@ -29,10 +29,6 @@
   this software.
 */
 
-#if (USE_INTERNAL_SERIAL == NO_DESCRIPTOR)
-	#warning USE_INTERNAL_SERIAL is not available on this AVR - please manually construct a device serial descriptor.
-#endif
-
 /** \file
  *
  *  USB Device Descriptors, for library use when in USB device mode. Descriptors are special 
@@ -42,6 +38,18 @@
 
 #include "Descriptors.h"
 
+/* On some devices, there is a factory set internal serial number which can be automatically sent to the host as
+ * the device's serial number when the Device Descriptor's .SerialNumStrIndex entry is set to USE_INTERNAL_SERIAL.
+ * This allows the host to track a device across insertions on different ports, allowing them to retain allocated
+ * resources like COM port numbers and drivers. On demos using this feature, give a warning on unsupported devices
+ * so that the user can supply their own serial number descriptor instead or remove the USE_INTERNAL_SERIAL value
+ * from the Device Descriptor (forcing the host to generate a serial number for each device from the VID, PID and
+ * port location).
+ */
+#if (USE_INTERNAL_SERIAL == NO_DESCRIPTOR)
+	#warning USE_INTERNAL_SERIAL is not available on this AVR - please manually construct a device serial descriptor.
+#endif
+
 /** HID class report descriptor. This is a special descriptor constructed with values from the
  *  USBIF HID class specification to describe the reports and capabilities of the HID device. This
  *  descriptor is parsed by the host and its contents used to determine what data (and in what encoding)

Demos/Device/ClassDriver/MassStorageKeyboard/makefile

@@ -123,8 +123,7 @@ LUFA_PATH = ../../../..
 
 
 # LUFA library compile-time options
-LUFA_OPTS  = -D USE_NONSTANDARD_DESCRIPTOR_NAMES
-LUFA_OPTS += -D USB_DEVICE_ONLY
+LUFA_OPTS  = -D USB_DEVICE_ONLY
 LUFA_OPTS += -D FIXED_CONTROL_ENDPOINT_SIZE=8
 LUFA_OPTS += -D FIXED_NUM_CONFIGURATIONS=1
 LUFA_OPTS += -D USE_FLASH_DESCRIPTORS
@@ -132,6 +131,7 @@ LUFA_OPTS += -D USE_STATIC_OPTIONS="(USB_DEVICE_OPT_FULLSPEED | USB_OPT_REG_ENAB
 LUFA_OPTS += -D INTERRUPT_CONTROL_ENDPOINT
 
 
+
 # List C source files here. (C dependencies are automatically generated.)
 SRC = $(TARGET).c                                                 \
 	  Descriptors.c                                               \