[Toybox] Add remaining pwd options

[Felix Janda]

Thanks for the various clarifications and making "pwd -L" check for dot
and dot-dot as described in the standard.

Looking at the POSIX man page toysh should set $PWD at some point, too.
Right now we have

$cd /tmp
$ln -s . a
$cd a
$cd ..
$pwd
/

whereas from my reading of POSIX the current working directory should be
/tmp at this point.

Felix

 1356864433.0