Let libnvpair be linked independently of libzfs.

Let libnvpair be linked independently of libzfs.

Autoconf will fail to detect the ZoL libnvpair on systems that do not
implicitly link library runtime dependencies, which is anything that
has the GCC 4.5 DCO update.

Build libuutil before libnvpair, and put it on the the LDADD line of
the libnvpair automake template.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes: #560