build: init submodules when calling autogen.sh

if one submodule is not initializied it will run submodule update --init
  --recursive, which will download the files that are needed.

The whole thing is also just called if you are in a git repository so
nothing of that magic is done when a tarbal is downloaded and shipped.

autogen.sh

@@ -3,6 +3,14 @@
 rm -rf autom4te.cache
 rm -f aclocal.m4 ltmain.sh
 
+if [ -d ".git"]; then
+    echo "Getting all submodules"
+    if [ $(git submodule status | cut -c1 | grep "-") ]; then
+        echo "A few submodules are not initializied."
+        echo "Calling 'git submodule update --init --recursive'"
+        git submodule update --init --recursive
+    fi
+fi
 echo "Running autopoint..." ; autopoint -f || :
 echo "Running aclocal..." ; aclocal -I m4 $ACLOCAL_FLAGS || exit 1
 echo "Running autoconf..." ; autoconf || exit 1