Disable device mapper support by default in FreeBSD.

Device mapper support is a Linux-specific extension, and not applicable
to FreeBSD where the necessary libraries do not exist.
Apply Debian patch "freebsd-geli.patch" as of version 2.3-12.
Apply Debian patch "freebsd-zvol.patch" as of version 2.3-12.
Apply Debian patch "freebsd-ufs.patch" as of version 2.3-12.
Apply Debian patch "kfreebsd-lvm.patch" as of version 2.3-12.
Fix incorrect error message in configure script.

We now support "freebsd" in addition to "linux", "gnu" and "beos".