Use "pwd -P" to get the current physical path.

It is a portable version of the realpath(1) utility that you can find on
Mac OS X and FreeBSD (see also The Open Group Base Specifications Issue
6, IEEE Std 1003.1).

Without the -P flag, pwd(1) might return different values when the
current path contains one or more symlinks, depending on how you got
into the current directory.

In simplenode.runner, this may cause PIPE_DIR to have different values
on each use, which will make it impossible to connect to the running
node unless you guess the correct path yourself.
Merge pull request #96 from olgeni/pwd-symlink-fix

Use "pwd -P" to get the current physical path.