build: ensure gem and tgz targets build manpages
Original patch by Hongli Lai <hongli@phusion.nl>:
> >From
bfefc2cf0efb0913a42862886363b3140dcdbb2a Mon Sep 17 00:00:00 2001
> From: Hongli Lai (Phusion) <hongli@phusion.nl>
> Date: Mon, 6 Jun 2011 13:39:00 +0200
> Subject: [PATCH] Ensure that 'make gem' builds the documentation too.
>
> If autogenerated documentation files, like man pages, don't exist then
> 'make gem' will fail, complaining that some files are not found. By
> depending the 'gem' target on the 'doc' target we ensure that 'make gem'
> always works.
>
> Signed-off-by: Hongli Lai (Phusion) <hongli@phusion.nl>
ref: http://mid.gmane.org/
4DED0EE2.
7040400@phusion.nl