function `rt_pin_write` is invoked by  function `can_bus_hook`, and it should to be initialized by gpio.c.
but gpio.c was not added in SConscript

enum CANBAUD was changed in components/drivers/include/drivers/can.h ,
which causes array index out of bound in bsp/stm32f10x/drivers/bxcan.c

temporarily remove RT_CAN_USING_BUS_HOOK, because there are some bugs in
bsp/stm32f10x/applications/canapp.c  function can_bus_hook

Update serial.c

fix reset serial receive interrupt flag when close serial

remove function finsh_set_device in application.c in bsp/stm32f10x

finsh_set_device is not needed since version 1.2.0

fix initialization error in bsp/stm32f10x

temporarily disable canapp initialization.

fix various bugs in lwip-nat

This bug causes buffer overrun.

LWIP_NAT_TMR_INTERVAL_SEC defined in ipv4_nat.h is in miliseconds,
but ip_nat_check_timeout() thinks it's in seconds.

With this bug, all nat entries will expire immediately when
ip_nat_check_timeout() is called.

Note sys_timeout() is in miliseconds.

SCons PreProcessor patch: Stop processing "#define" in false condition

Example "rtconfig.h" content:
 ...
 //#define BOARD_USING_LED
 #if defined(BOARD_USING_LED)
 #define RT_USING_RTGUI
 #endif
 ...

- Before patching, RTGUI module will be built although not intend to do so.
- After patching, RTGUI module will not be built.

fixed Lwip bug: Assert on TCP netconn_write with sndtimeout set

ref: http://savannah.nongnu.org/bugs/?38219

[DFS] Fix the ramfs issue.

修正components.h中使能RT_USING_DFS_RAMFS宏时，加入ramfs.h头文件