[4.0] 9acf7dc Increase Sphinx strictness.

[Lasse Karstensen]

commit 9acf7dccf0f768ee265454364fc3a66e8beb5011
Author: Lasse Karstensen <lkarsten at varnish-software.com>
Date:   Tue May 13 13:59:01 2014 +0200

    Increase Sphinx strictness.
    
    Warnings are now considered build errors.
    
    We've been shipping documentation with sections missing
    because we didn't take warnings seriously.
    
    Bonus change: build in parallel, save 82 centiseconds per build!
    (html target on my laptop, ymmv)

diff --git a/doc/sphinx/Makefile.am b/doc/sphinx/Makefile.am
index 0219fac..a5b9718 100644
--- a/doc/sphinx/Makefile.am
+++ b/doc/sphinx/Makefile.am
@@ -3,7 +3,7 @@
 
 # You can set these variables from the command line.
 SPHINXOPTS    =
-SPHINXBUILD   = sphinx-build
+SPHINXBUILD   = sphinx-build -j4 -W -N -n
 PAPER         = a4
 BUILDDIR      = build