kernel/timer: change row_lvl to unsigned

Use signed int as array index is unsecure.
msh: check path is non-null in msh_auto_complete_path
msh: free is only available when HEAP is enabled
dfs: check for null reference
minilibc: only define malloc family when RT_USING_HEAP enabled
Merge pull request #353 from grissiom/misc-fix

Misc fix
Add mb9bf568r to bsp
Merge pull request #356 from yangfasheng/master

Add mb9bf568r to bsp
finsh: allow user to disable the FINSH_USING_HISTORY
Merge pull request #357 from grissiom/enhance-finsh

finsh: allow user to disable the FINSH_USING_HISTORY
[GDB] Fix compiling error when not enable GDB.
[LIBC] Use RT_USING_LIBC instead of libs option for each compiler
[BSP] use RT_USING_LIBC instead of RT_USING_NEWLIB
Merge pull request #360 from BernardXiong/master

[LIBC] Use RT_USING_LIBC instead of libs option for each compiler
[LIBC] fix the fopen/open issue in armlibc
[C++] Add cplusplus component
[Drivers] Add sensor framework
Merge remote-tracking branch 'upstream/master'
[BSP] use RT_USING_LIBC instead of RT_USING_NEWLIB
[BSP] Update C++ compiling options