build manuals moved here from osmo-gsm-manuals.git

Moved to doc/manuals/, with full commit history, in preceding merge commit.
Now incorporate in the build system.

Build with:

$ autoreconf -fi
$ ./configure --enable-manuals
$ make

Shared files from osmo-gsm-manuals.git are found automatically if
- the repository is checked out in ../osmo-gsm-manuals; or
- if it osmo-gsm-manuals was installed with "make install"; or
- OSMO_GSM_MANUALS_DIR is set.

Related: OS#3385
Change-Id: I504f05a49721f2dfe105b6c5fd1995c4e7a0be9c
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 5a23107..15f36b7 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -1,3 +1,4 @@
 SUBDIRS = \
 	examples \
+	manuals \
 	$(NULL)
diff --git a/doc/manuals/Makefile b/doc/manuals/Makefile
deleted file mode 100644
index b092e66..0000000
--- a/doc/manuals/Makefile
+++ /dev/null
@@ -1,10 +0,0 @@
-TOPDIR = ..
-
-ASCIIDOC = osmomgw-usermanual.adoc
-ASCIIDOC_DEPS = chapters/*.adoc
-include $(TOPDIR)/build/Makefile.asciidoc.inc
-
-VTY_REFERENCE = osmomgw-vty-reference.xml
-include $(TOPDIR)/build/Makefile.vty-reference.inc
-
-include $(TOPDIR)/build/Makefile.common.inc
diff --git a/doc/manuals/Makefile.am b/doc/manuals/Makefile.am
new file mode 100644
index 0000000..901cffa
--- /dev/null
+++ b/doc/manuals/Makefile.am
@@ -0,0 +1,16 @@
+EXTRA_DIST = osmomgw-usermanual.adoc \
+    osmomgw-usermanual-docinfo.xml \
+    osmomgw-vty-reference.xml \
+    chapters \
+    vty
+
+if BUILD_MANUALS
+  ASCIIDOC = osmomgw-usermanual.adoc
+  ASCIIDOC_DEPS = $(srcdir)/chapters/*.adoc
+  include $(OSMO_GSM_MANUALS_DIR)/build/Makefile.asciidoc.inc
+
+  VTY_REFERENCE = osmomgw-vty-reference.xml
+  include $(OSMO_GSM_MANUALS_DIR)/build/Makefile.vty-reference.inc
+
+  include $(OSMO_GSM_MANUALS_DIR)/build/Makefile.common.inc
+endif
diff --git a/doc/manuals/osmomgw-usermanual.adoc b/doc/manuals/osmomgw-usermanual.adoc
index 6030023..b0bc83d 100644
--- a/doc/manuals/osmomgw-usermanual.adoc
+++ b/doc/manuals/osmomgw-usermanual.adoc
@@ -6,28 +6,28 @@
 Daniel Willmann <dwillmann@sysmocom.de>
 
 
-include::../common/chapters/preface.adoc[]
+include::./common/chapters/preface.adoc[]
 
-include::chapters/overview.adoc[]
+include::{srcdir}/chapters/overview.adoc[]
 
-include::chapters/running.adoc[]
+include::{srcdir}/chapters/running.adoc[]
 
-include::../common/chapters/vty.adoc[]
+include::./common/chapters/vty.adoc[]
 
-include::../common/chapters/logging.adoc[]
+include::./common/chapters/logging.adoc[]
 
-include::chapters/configuration.adoc[]
+include::{srcdir}/chapters/configuration.adoc[]
 
-include::chapters/mgcp_extensions.adoc[]
+include::{srcdir}/chapters/mgcp_extensions.adoc[]
 
-//include::chapters/counters.adoc[]
+//include::{srcdir}/chapters/counters.adoc[]
 
-include::../common/chapters/port_numbers.adoc[]
+include::./common/chapters/port_numbers.adoc[]
 
-include::../common/chapters/bibliography.adoc[]
+include::./common/chapters/bibliography.adoc[]
 
-include::../common/chapters/glossary.adoc[]
+include::./common/chapters/glossary.adoc[]
 
-include::../common/chapters/gfdl.adoc[]
+include::./common/chapters/gfdl.adoc[]
 
 
diff --git a/doc/manuals/osmomgw-vty-reference.xml b/doc/manuals/osmomgw-vty-reference.xml
index 2d91545..334453e 100644
--- a/doc/manuals/osmomgw-vty-reference.xml
+++ b/doc/manuals/osmomgw-vty-reference.xml
@@ -5,7 +5,7 @@
 -->
 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML 5.0//EN"
 "http://docbook.org/xml/5.0/dtd/docbook.dtd" [
-<!ENTITY chapter-vty      SYSTEM      "../common/chapters/vty.xml" >
+<!ENTITY chapter-vty      SYSTEM      "./common/chapters/vty.xml" >
 <!ENTITY sections-vty     SYSTEM      "generated/docbook_vty.xml"  >
 ]>