[YModem] YModem optimization;
[BSP] Add more error handling in STM32F1 bsp. 

[bsp] Fix the spelling errors. 

drvers->drivers

update RW009 driver.

Remove unsupport syntex for python 2.6.

Dict Comprehensions is imported in Python 2.7 & 3.0 which is PEP 274 [1]. Some
OS like CentOS 6 which is use Python 2.6 cannot support this syntex.

[1] http://legacy.python.org/dev/peps/pep-0274/Signed-off-by: NXiongfei Guo <xfguo@credosemi.com>

kernel/idle: fix rt_thread_idle_excute in high optimization level

The rt_list_isempty has prototype of "int rt_list_isempty(const rt_list_t *l)".
So the compiler has a good reason that the rt_thread_defunct list does
not change within rt_thread_idle_excute thus optimize the "while" loop
into a "if".

So add the volatile qualifier when test against the rt_thread_defunc list.

[Serial] BUG Fix: data be send twice in mode that other than polling

minilibc: define SIZE_MAX in stdint.h

tools/building: remove the use of startupinfo

The startupinfo does not have any visible effects on the building
process and some old Python version does not have it at all. So remove
it for the seek of simple.

Tested `scons -j4` in a dual core virtual machine.

Add conditional compilation about IPv6 sources and headers, change code style

correct netconn API usage

fix:comment spelling mistake

[net] Add lwIP head porting to fetch lwIP new feature, for example IPv4/v6 dual stack.