INSTANCE_HOME, resolving any symlinks in any element within paths
        passed in via the INSTANCE_HOME or SOFTWARE_HOME envvars.  Paths that
        are computed by "dead reckoning" from os.getcwd and module paths are
        also "realpathed".  So for instance, if you use '/home/chrism/Instance'
        as your INSTANCE_HOME, and '/home/chrism' is a symlink to
        '/other/home/chrism', your INSTANCE_HOME will be computed as
        '/other/home/chrism/Instance'.  This is necessary to avoid
        weirdnesses while using "dead reckoning" from INSTANCE_HOME and
        SOFTWARE_HOME in other parts of the code.  POSIX systems only.