Create the third 0.6.0 release candidate tag (rc3).

Create the second 0.6.0 release candidate tag (rc2).

Create the first 0.6.0 release candidate tag (rc1).  The Posix
layer is now functional and passes fstest and several other
test suites cleanly.  We now need this release candidate tag
to broaden the test coverage before we can release the official
zfs-0.6.0.

Roll the version forward to 0.6.0, the addition of the Posix
layer warrents updating the major version number.

Update META file to prep for 0.5.2 tag.

Add autoconf style build infrastructure to the ZFS tree.  This
includes autogen.sh, configure.ac, m4 macros, some scripts/*,
and makefiles for all the core ZFS components.