Make gtk-doc not a hard dependency of GLib

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=674314

autogen.sh

@@ -7,10 +7,13 @@ test -n "$srcdir" || srcdir=.
 olddir=`pwd`
 cd "$srcdir"
 
-GTKDOCIZE=`which gtkdocize`
+GTKDOCIZE=$(which gtkdocize 2>/dev/null)
 if test -z $GTKDOCIZE; then
-        echo "*** No GTK-Doc found, please install it ***"
-        exit 1
+        echo "You don't have gtk-doc installed, and thus won't be able to generate the documentation."
+        rm -f gtk-doc.make
+        echo 'EXTRA_DIST =' > gtk-doc.make
+else
+        gtkdocize || exit $?
 fi
 
 AUTORECONF=`which autoreconf`
@@ -24,7 +27,6 @@ fi
 # regenerated from their corresponding *.in files by ./configure anyway.
 touch README INSTALL
 
-gtkdocize || exit $?
 autoreconf --force --install --verbose || exit $?
 
 cd "$olddir"

configure.ac

@@ -2585,8 +2585,13 @@ AS_IF([ test $cross_compiling = yes && test x$enable_modular_tests = xyes], [
 dnl **************************
 dnl *** Checks for gtk-doc ***
 dnl **************************
-
+# gtkdocize greps for ^GTK_DOC_CHECK and parses it, so you need to have
+# it on it's own line.
+m4_ifdef([GTK_DOC_CHECK], [
 GTK_DOC_CHECK([1.15], [--flavour no-tmpl])
+],[
+AM_CONDITIONAL([ENABLE_GTK_DOC],[false])
+])
 
 AC_ARG_ENABLE(man,
               [AC_HELP_STRING([--enable-man],

docs/Makefile.am

@@ -1,7 +1,9 @@
 ## Process this file with automake to produce Makefile.in
 include $(top_srcdir)/Makefile.decl
 
+if ENABLE_GTK_DOC
 SUBDIRS = reference
+endif
 
 EXTRA_DIST += debugging.txt macros.txt