create POTFILES.in in autogen.sh script

autogen.sh

 #!/bin/sh
 set -x
+  echo "[encoding: UTF-8]" > po/POTFILES.in \
+  && ls data/gajim.desktop.in.in data/glade/*.glade \
+  src/*py src/common/*py src/common/zeroconf/*.py -1 -U >> \
+  po/POTFILES.in || exit 1
   intltoolize --force --automake \
   && aclocal -I ./m4 \
   && libtoolize --copy --force --automake \