[scons] fix the BSP_ROOT issue in ua.py.
[msh] try to complete module path

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.
[msh] cd to path when possible

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.
Merge pull request #249 from grissiom/msh-next

Msh next
Add PNG_ABORT for libpng; Add format field in tjpgd;
[msh] don't complain on empty command

Just branch out and no complain on command length == 0;
Merge pull request #250 from grissiom/msh-next

[msh] don't complain on empty command
[Kernel] Change the version number to 2.0.0.