new setup in cvs

[DJ Delorie]

I've just checked in my biggie patches to do these:

	* tar.c: New file; built-in tar using zlib.
	* tar.h: New file; header for same.
	* ctar.c: New file; test program for same.
	* Makefile.in: add built-in tar, remove tar.exe and gzip.exe
	* path.c (pathcat): convert slashes and canonicalize, instead of aborting
	* setup.c (tarx): add support for built-in tar
	(main): accept unix-style slashes, check root dir for drive letters,
	warn about installing in /, make sure cwd is empty for internet installs,
	defer mounts to end of install, support built-in tar.

One advantage I didn't think of before is that by using an internal
tar, we can defer messing with the mount table until after we know
everything was installed correctly.  Changing the mount table is now
the *last* thing setup does.

My next chunk will hopefully include these goals:

* internalize the remaining .exes
* use unique name and shared memory area for cygwin1.dll
* call cygwin1.dll functions directly (to internalize exe's above)
* default mount points to previously installed text/binary setting

This should also let setup run with an incompatible cygwin DLL already
running in the system.