[gnome-subtitles/wip/piotrdrag/port-to-yelp] Updating autogen.sh file for yelp-tools use

[Pedro Castro <pcastro src gnome org>]

commit 51db4a89e3c02e2eed8b5405ad1bc5df7634c66c
Author: Pedro Castro <pedro gnomesubtitles org>
Date:   Sun Oct 14 21:12:47 2018 +0100

    Updating autogen.sh file for yelp-tools use

 autogen.sh | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/autogen.sh b/autogen.sh
index cf9b746..d970d07 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -8,6 +8,13 @@ if [ ! -f "$srcdir/configure.ac" ]; then
  exit 1
 fi
 
+GNOMEDOC=`which yelp-build`
+if test -z $GNOMEDOC; then
+        echo "*** The tools to build the documentation are not found,"
+        echo "    please intall the yelp-tool package ***"
+        exit 1
+fi
+
 which gnome-autogen.sh || {
        echo "You need to install gnome-common"
        exit 1