1. Add macro check in rtdebug.h;
2. Use RT_USING_POSIX for poll/select, stdin etc.
3. Split dfs_posix.h to dfs_posix.h, dfs_poll.h and dfs_select.h;

[bsp] Fix compile error.

[bsp][lm3s8962] Fix complie error. Add missing macro RT_USING_LIBC. Force use Lwip 1.4.1 bye define RT_USING_LWIP141

[DFS][NFS] Fix compile error. Move nfs_file/nfs_dir data ptr into struct nfs_filesystem

[BSP] fix the compiling issue.

[components][net] In SConscript file, replace RT_USING_LWIP140 with RT_USING_LWIP141

1. Change the type of cmd to 'int';
2. Remove RT_LWIP_USING_RT_MEM macro;

1. Remove RT_LWIP_USING_RT_MEM option;
2. Add waitqueue patch for lwIP 2.0.2;

1. Change 'rt_uint8_t' type of cmd to 'int';
2. Add waitqueue;
3. Split device ipc header files;

1. Add poll/select APIs;
2. Add wait queue implementation;
3. Remove DFS_STATUS_* code and use errno;
4. Add pipe API;
5. Use a standalone fops in DFS;

1. Add POSIX termios implementation;
2. Add POSIX signals implementation;
3. Add stdio for each libc.

1. Add signal implementation;
2. Change the 'rt_uint8_t' of cmd to 'int';

1. Remove components.h file;
2. Add libc_* files for standard libc definitions;
3. Add rtdbg.h file for simple debug log;
4. Add single list implementation;
5. Change the 'rt_uint8_t' type of cmd to 'int'.

[Finsh] Stop push new history when current cmd is same as last cmd.