Enable cwd and chdir methods allowing '.' and '..'

[d-w-moore]

Like icommands, PRC could keep a memory of current working directory per-session. Methods could be added to resolve relative paths including . and .. as path elements. In doing this, the relative path would be translated to absolute path by appending it to the current working directory and normalizing to create suitable path-string parameter, applicable wherever PRC requires a logical path.

irods.path.iRODSPath , which was developed to support #323, can support this as well.