for 2013-02-20 aozima commmit "port for gcc", but the commit is
not tested,and the kernel is breakdown in context_gcc.S, the file
is a copy from cortex-m3,but not port for cortex-m0, so i complete
this port for aozima, test it in stm32f0discovery board ,
and it works fine.

simulatr: print error messages when RTT_RTGUI is invalid

Revert "serial: set the errno if and only if in thread context"

This reverts commit 07bd09fc.
The validation of the context is done with in `rt_set_errno`. So it's
safe to call it here.

Serial fix

The errno is associated with threads. It will crash the thread if we set
it in interrupt context.

Return early if the size is 0 as there is nothing to do.

K60: fix compile error

Log trace in mem

Rm48x50 next

After `log_trace_init()`, call `memlog_init`. It then turn the logtrace
into a "in-memory" logger which will buffer all the log in memory. It
also set a hook in idle to flush all the log into console. One may
create an other thread to flush the logs but idle might be the simplest
place to go.

initialize timer in bsp

With new timer algorithm, timer should be initialized during startup. So
add them to the bsps. Use these commands to get which bsp is missing
calling the function:

    % git grep rt_system_timer_init bsp|sed -n 's|bsp/\([^/]*\).*|\1|p' | sort | uniq > have_tm_init
    % ls -1 bsp |sed -n 's|\([^/]*\).*|\1|p' | sort > all_bsp
    % comm -3 all_bsp have_tm_init
    beaglebone
    lpc176x
    lpc178x
    ls1bdev
    mb9bf506r
    stm32f10x
    xplorer4330

We could not handle any traps except IRQ/FIQ.

kernel: timer: fix compiling bug in d59aa279

Finsh ex

We split the history handling form the key handling. So we could handle
the direction key even if the history is disabled. As a "side effect", I
also remove the unnecessary "use_history" bit.

kernel: use skip list to implement timer list

make sure the device is in STREAM mode when used by rt_kprintf.

UART DMA tx_complete() with buffer information

simulator/jffs2: remove _TIME_T_DEFINED when built by VC++

_TIME_T_DEFINED was pre-defined in order to build jffs2 with VC.
While it may cause many side effects.

simulator: add createdef.py to generate def file for VS

kernel: mutex could only be released in thread context

Now we can get rid off Mingw to create def file. To create def file, one
should run:

    scons --def

in the bsp/simulator.

Mutex has the idea of ownership, only the thread which owns the mutex
can release it. So rt_mutex_release could only be called in thread
context.  Add a debug guard to it.

Skip list is a "random" data structure that in high possibilities it
would get O(log(N)) time complexity in inserting while the old list get
O(N). Forthermore, when set RT_TIMER_SKIP_LIST_LEVEL to 1, it will just
the same as the old double linked list, both in time and space
complexity.

Benchmarks shows that when RT_TIMER_SKIP_LIST_LEVEL is 3, the average
time of random insertion of new timer is about 2 times faster than the
old timer when there are 100 timers and 3 times faster when there are
200 timers.

However, it restores the deprecated funcion rt_system_timer_init. BSPs
must invoke it upon system startup.

kernel: fix compiling error when RT_DEBUG is not defined

Define RT_DEBUG_IN_THREAD_CONTEXT when RT_DEBUG is not defined.