Add options to enable/disable docs and demos

Originally written by Anthony Viallard
<viallard@syscom-instruments.com>.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: gnuplot-4.6.0/configure.in
===================================================================
--- gnuplot-4.6.0.orig/configure.in	2012-03-08 05:34:42.000000000 +0100
+++ gnuplot-4.6.0/configure.in	2013-01-07 11:50:03.003804463 +0100
@@ -748,6 +748,16 @@
 AC_ARG_WITH(lisp-files,dnl
 [  --without-lisp-files    do not build emacs lisp files])
 
+dnl Whether we want to build the demo files
+dnl Does nothing here, is passed on to the demo subdir
+AC_ARG_ENABLE(demo,dnl
+[  --disable-demo    do not build demo files])
+
+dnl Whether we want to build the doc files
+dnl Does nothing here, is passed on to the doc subdir
+AC_ARG_ENABLE(doc,dnl
+[  --disable-doc    do not build doc files])
+
 dnl Sort help/subtopic tables by row or column
 AC_ARG_WITH(row-help,dnl
 [  --with-row-help         format help and subtopic tables by row (default)
@@ -1200,6 +1210,24 @@
 fi
 AC_SUBST(LISPDIR)
 
+dnl build demo files
+if test "$enable_demo" != no; then
+  AC_CONFIG_SUBDIRS(demo)
+  DEMOSUBDIR=demo
+else
+  DEMOSUBDIR=
+fi
+AC_SUBST(DEMOSUBDIR)
+
+dnl build doc files
+if test "$enable_doc" != no; then
+  AC_CONFIG_SUBDIRS(docs)
+  DOCSUBDIR=docs
+else
+  DOCSUBDIR=
+fi
+AC_SUBST(DOCSUBDIR)
+
 dnl Substitute variables
 AC_SUBST(PACKAGE)
 AC_SUBST(VERSION_MAJOR)
Index: gnuplot-4.6.0/Makefile.am
===================================================================
--- gnuplot-4.6.0.orig/Makefile.am	2013-01-04 14:07:02.239120935 +0100
+++ gnuplot-4.6.0/Makefile.am	2013-01-07 11:51:12.034846363 +0100
@@ -1,7 +1,7 @@
 ## Process this file with automake to produce Makefile.in -*-Makefile-*-
 AUTOMAKE_OPTIONS = foreign 1.2h
 
-SUBDIRS = config m4 term src docs $(LISPDIR) man demo tutorial share
+SUBDIRS = config m4 term src $(DOCSUBDIR) $(LISPDIR) man $(DEMOSUBDIR) tutorial share
 
 EXTRA_DIST = BUGS CodeStyle Copyright FAQ.pdf GNUmakefile INSTALL INSTALL.gnu \
 Makefile.maint PATCHLEVEL PGPKEYS PORTING README README.1ST \