DFS: add dfs_file_flush prototype in dfs_file.h
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
Merge pull request #170 from grissiom/rtt-next

kernel: add RT_DEBUG_IN_THREAD_CONTEXT
kernel: fix compiling error when RT_DEBUG is not defined

Define RT_DEBUG_IN_THREAD_CONTEXT when RT_DEBUG is not defined.