Bug 4877 [ENH] [SIGNED-OFF] install generated man pages with build process

Bug 4877 [ENH] [SIGNED-OFF] install generated man pages with build process

This uses the docbook source files to generate the man pages, and
installs them to their correct location when the packages are being
built.

This will make it easier for people to write man pages, thereby ensuring
that people join in keeping documentation up to date.

Note: adds docbook-xsl and xsltproc to the dependencies.
Note2: applies on top of Magnus' other patch on this ticket.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>