configure.ac : disable doc by default and check for asciidoc

This is a complaint that has been reported many many times. By default, docs
are enabled and there is no check for asciidoc, so anyone building from git
will see their build fail.

We cannot do a strict check for asciidoc because released source tarballs
have man pages already built, and it should be possible to install them
without having asciidoc.

This patch attempts to improve the situation in two ways :
1) disable doc by default
2) print a warning if docs are enabled but asciidoc is not installed

Signed-off-by: Xavier Chantry <chantry.xavier@gmail.com>
Signed-off-by: Dan McGee <dan@archlinux.org>

configure.ac

@@ -100,8 +100,8 @@ AC_ARG_ENABLE(internal-download,
 
 # Help line for documentation
 AC_ARG_ENABLE(doc,
-	AS_HELP_STRING([--disable-doc], [prevent make from looking at doc/ dir]),
-	[wantdoc=$enableval], [wantdoc=yes])
+	AS_HELP_STRING([--enable-doc], [run make in doc/ dir]),
+	[wantdoc=$enableval], [wantdoc=no])
 
 # Help line for doxygen
 AC_ARG_ENABLE(doxygen,
@@ -261,12 +261,18 @@ AC_SUBST(CARCHFLAGS)
 AC_SUBST(CHOST)
 
 # Check for documentation support and status
+AC_CHECK_PROGS([ASCIIDOC], [asciidoc])
 AC_MSG_CHECKING([for building documentation])
 if test "x$wantdoc" = "xyes" ; then
-	AC_MSG_RESULT([yes])
+	if test $ASCIIDOC ; then
+		AC_MSG_RESULT([yes, enabled by configure])
+	else
+		asciidoc="(warning : asciidoc not installed)"
+		AC_MSG_RESULT([yes $asciidoc])
+	fi
 	wantdoc=yes
 else
-	AC_MSG_RESULT([no, disabled by configure])
+	AC_MSG_RESULT([no])
 	wantdoc=no
 fi
 AM_CONDITIONAL(WANT_DOC, test "x$wantdoc" = "xyes")
@@ -389,7 +395,7 @@ ${PACKAGE_NAME}:
     build script name      : ${BUILDSCRIPT}
 
   Compilation options:
-    Run make in doc/ dir   : ${wantdoc}
+    Run make in doc/ dir   : ${wantdoc} ${asciidoc}
     Use download library   : ${internaldownload}
     Doxygen support        : ${usedoxygen}
     debug support          : ${debug}