* $PWD was used if it appeared ``correct''. this `enhancment' was
not documented in getcwd(3), and caused problems for pwd(1) (which
uses getcwd(3)), and in turn <bsd.obj.mk> (which uses pwd) when $PWD
is set to the logical path instead of the real path (e.g, symlink
/usr/src -> /z/NetBSD-current/src).
[$PWD is set to the logical path by tcsh(1) with set symlinks=expand]
* as getcwd() without the $PWD code is just a wrapper to getcwd_physical(),
rename the latter to the latter. hack realpath() to use the getcwd().
yet another case of `it was a good idea, but...'