because it's potentially dangerous (think: symlink races). Move
realpath() back to it's original location, and remove getcwd_physical()
by renaming it back to getcwd() and zapping the original getcwd wrapper.
Noticed by: bde
Performance is comparable to gnumalloc if you have sufficient RAM, and
it screams around it if you don't.
Compiled with "EXTRA_SANITY" until further notice.
see malloc.3 for more details.