Make it build on Debian (Wheezy).

This patch set fixes a number of build issues on Debian.

- Missing build dependency on python-setuptools
- The Makefile gets invokes multiple times with the default target (first target).  The install target should not be used multiple times.  Create a default rule that does nothing.
- The Makefile has a number of problems:
  - It uses spaces instead of tabs for indentation.
  - It should emit a useful error message if DESTDIR is empty.
  - The arguments to tar are in the wrong order (x needs to come earlier).
- Files should be installed in /usr, not /usr/local. I get the following error message:

    dh_usrlocal: debian/zfs-tools/usr/local/bin/zfs-shell is not a directory
    dh_usrlocal: debian/zfs-tools/usr/local/bin/zreplicate is not a directory
    dh_usrlocal: debian/zfs-tools/usr/local/bin/zsnap is not a directory
    rmdir: failed to remove `debian/zfs-tools/usr/local/bin': Directory not empty
    dh_usrlocal: rmdir debian/zfs-tools/usr/local/bin returned exit code 1
    make: *** [binary] Error 1
    dpkg-buildpackage: error: fakeroot debian/rules binary gave error exit status 2

- On Debian the zfs package is either zfs-fuse or debian-zfs (if using ZoL).