Pull in latest man pages as part of update-zfs.sh

The script has been updated to download the latest documentations
packages for Solaris and extract the needed ZFS man pages. These
will still need a little markup to handle changes between the
Solaris and Linux versions of ZFS. Howver, they should be pretty
minor I've tried hard to keep the interface the same.

In additional to the script update the zdb, zfs, and zpool man
pages have been added to the repo.