add /opt/local/share/xsl/docbook-xsl-nons to the places to look for...

add /opt/local/share/xsl/docbook-xsl-nons to the places to look for manpages/docbook.xsl under macports

(cherry picked from commit 74252522)
13 jobs for 453-master-build-broken-in-documentation-tree-v9_12 in 8 minutes and 57 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Precheck
passed precheck:debian:sid:amd64 #30737
amd64 docker linux

00:00:15

 
  Build
passed build:centos:centos6:amd64 #30738
amd64 docker linux

00:02:16

passed build:centos:centos7:amd64 #30739
amd64 docker linux

00:02:35

passed build:debian:sid:amd64 #30740
amd64 docker linux

00:01:51

passed build:debian:sid:i386 #30741
i386 docker linux

00:01:54

 
  Test
passed systemtest:centos:centos6:amd64 #30746
amd64 docker linux

00:05:16

passed systemtest:centos:centos7:amd64 #30747
amd64 docker linux

00:05:15

passed systemtest:debian:sid:amd64 #30748
amd64 docker linux

00:05:17

passed systemtest:debian:sid:i386 #30749
i386 docker linux

00:05:39

passed unittest:centos:centos6:amd64 #30742
docker linux amd64

00:00:56

passed unittest:centos:centos7:amd64 #30743
amd64 docker linux

00:00:56

passed unittest:debian:sid:amd64 #30744
amd64 docker linux

00:00:51

passed unittest:debian:sid:i386 #30745
i386 docker linux

00:00:53