[msh] don't complain on empty command

Just branch out and no complain on command length == 0;

When DFS_USING_WORKDIR is enabled, msh will try to chdir if the command
is not found. For example, if there is folder named "SD", and there is
no `SD` command and `SD.mo` module, typing "SD" in msh will cd to the
folder.

In more detail, the execution order right now is:

1. built-in command
2. module
3. cd to path

If you have a folder named "ps", you have to run `cd ps` to change the
working dir.

Msh can execute module directly. So try to auto-complete the path when
user press TAB. There is a chance that the path is a module.

2.adjust some viable and micro name
3.some other small fix

This reverts commit 5aeedc4f3a, reversing
changes made to 3d80e414ff.

This merge breaks every uart driver in all BSPs. @bright-pan , is there
any way to get this done without breaking existing code?

Add hardware flow support.
Use new struct serial_ringbuffer.

Pass USB CV test verification;
Code cleanup;

This issue causes fstat & lseek not correct.

update CMSIS version to 3.20

fix msh_exec(char* cmd, rt_size_t length) bug

I have to mention that this bug is introduced by myself, in the last
commit <fd07f30f511335f506ae6557e300093d4dde421e> to dfs_nfs.c

fix dfs_unmount bug

more infomation:
http://www.rt-thread.org/phpBB3/topic2965.html

fix #211

empty is confused in dfs_filesystem_lookup.

clean code with pointer rather than index

decrease indentation to make cleaner code
fix mkfs bug when there is no mkfs implementation

1. rt_console_get_device should be call to set shell device only when it is null, or it will make finsh_set_device useless.
2. RT_USING_CONSOLE can be disabled in bsp/rtconfig.h

On Windows platform, please set `autocrlf = true` and on Linux, please
set `autocrlf = input`.

Signed-off-by: armink <armink.ztl@gmail.com>

Signed-off-by: armink <armink.ztl@gmail.com>

This reverts commit 07bd09fc0f.
The validation of the context is done with in `rt_set_errno`. So it's
safe to call it here.

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.

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.

UART DMA tx_complete() with buffer information

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

DFS: add dfs_file_flush prototype in dfs_file.h

The first parameter of memmove is the dst, not src. Besides, fix the
wrong move size.