man: generate configured paths in manpages

In particular, use /lib/systemd instead of /usr/lib/systemd in distributions
like Debian which still have not adopted a /usr merge setup.

Use XML entities from man/custom-entities.ent to replace configured paths while
doing XSLT processing of the original XML files. There was precedent of some
files (such as systemd.generator.xml) which were already using this approach.

This addresses most of the (manual) fixes from this patch:
http://anonscm.debian.org/cgit/pkg-systemd/systemd.git/tree/debian/patches/Fix-paths-in-man-pages.patch?h=experimental-220

The idea of using generic XML entities was presented here:
http://lists.freedesktop.org/archives/systemd-devel/2015-May/032240.html

This patch solves almost all the issues, with the exception of:
- Path to /bin/mount and /bin/umount.
- Generic statements about preference of /lib over /etc.

These will be handled separately by follow up patches.

Tested:
- With default configure settings, ran "make install" to two separate
  directories and compared the output to confirm they matched exactly.
- Used a set of configure flags including $CONFFLAGS from Debian:
  http://anonscm.debian.org/cgit/pkg-systemd/systemd.git/tree/debian/rules
  Installed the tree and confirmed the paths use /lib/systemd instead of
  /usr/lib/systemd and that no other unexpected differences exist.
- Confirmed that `make distcheck` still passes.

1 files changed, 6 insertions, 3 deletions

diff --git a/man/udev.xml b/man/udev.xml
index d1a4f614cf..f7ebaad4bc 100644
--- a/man/udev.xml
+++ b/man/udev.xml
@@ -1,6 +1,9 @@
 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
-  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
+<!ENTITY % entities SYSTEM "custom-entities.ent" >
+%entities;
+]>
 
 <refentry id="udev">
   <refentryinfo>
@@ -55,7 +58,7 @@
 
   <refsect1><title>Rules Files</title>
       <para>The udev rules are read from the files located in the
-      system rules directory <filename>/usr/lib/udev/rules.d</filename>,
+      system rules directory <filename>&udevlibexecdir;/rules.d</filename>,
       the volatile runtime directory <filename>/run/udev/rules.d</filename>
       and the local administration directory <filename>/etc/udev/rules.d</filename>.
       All rules files are collectively sorted and processed in lexical order,
@@ -421,7 +424,7 @@
                 <listitem>
                   <para>Execute an external program specified as the assigned
                   value. If no absolute path is given, the program is expected
-                  to live in <filename>/usr/lib/udev</filename>; otherwise, the
+                  to live in <filename>&udevlibexecdir;</filename>; otherwise, the
                   absolute path must be specified.</para>
                   <para>This is the default if no <replaceable>type</replaceable>
                   is specified.</para>