configure.ac - allow user to switch off/on documentation generation

configure.ac - allow user to switch off/on documentation generation

Andrian Nord <NightNord@gmail.com>:
>> > > As documentation requires docbook2man to be installed, which is not,
>> > > otherwise, required for proper LXC work or compilation process, it
>> > > might be usefull to be able to switch it off.

Michel Normand <normand@fr.ibm.com>:
> > For me, it is Ok to add a --enable/disable/-doc,
> > but not make configure to fail if no option specified
> > and no docbook2man package.
> >
> > For me it should be optionnal.
> > I like the current behaviour where configure is running without option
> > and is enabling/disabling by itself the doc building.
> > Could you send a new patch with this idea ?

Andrian Nord <NightNord@gmail.com>:
Of course. You mean, that you what default behaviour to remain
auto-detection? That is:
--enable-doc: require docbook2man or fail, generate mans
--enable-doc=auto, or not specified (default): check for docbook2man,
generate mans if found, silently ignore if not found (I suppose
diagnostic message is redundant, as information already contains into
./configure --help)
--disable-doc: never check for docbook2man and don't gen mans

Here comes a patch what do this, as far as I see
(I'm sorry for violating post-rules in previous mail, now I'll do all
right, I hope. Should I attach patch anyway, as it might be usefull
for applying?)

Signed-off-by: Andrian Nord <NightNord@gmail.com>
Acked-by: Michel Normand <normand@fr.ibm.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>