log_trace: fix the memmove use

The first parameter of memmove is the dst, not src. Besides, fix the
wrong move size.
Merge pull request #169 from grissiom/log_trace-fix

log_trace: fix the memmove use
Merge pull request #168 from grissiom/dfs-fix

DFS: add dfs_file_flush prototype in dfs_file.h
kernel: add RT_DEBUG_IN_THREAD_CONTEXT

In thread context means: 1) the scheduler has been started; 2) not in
interrupt context. It is more stronger than RT_DEBUG_NOT_IN_INTERRUPT.
With this commit, you will catch the error on situations like taking
mutex before scheduling instead of crashing on NULL pointer reference.
Merge pull request #170 from grissiom/rtt-next

kernel: add RT_DEBUG_IN_THREAD_CONTEXT
DFS: cleanup mount/unmount code

Rename the label "err1" to "out_unlock".
DFS: let mount failed on rt_device_open error