python/python-dateutil: add python3 as an optional dependency

Signed-off-by: Larry Hajali <larryhaja[at]gmail[dot]com>

python/python-dateutil/README

@@ -1,2 +1,7 @@
 The dateutil module provides powerful extensions to the
 standard datetime module.
+
+Note: To install python3 bindings install six with python3
+bindings and pass PYTHON3=yes to the slackbuild.
+
+  # PYTHON3=yes ./python-dateutil.SlackBuild

python/python-dateutil/python-dateutil.SlackBuild

@@ -64,6 +64,11 @@ done
 
 python setup.py install --root=$PKG
 
+# Install python3 bindings. Default is no.
+if [ "${PYTHON3:-no}" == "yes" ]; then
+  python3 setup.py install --root=$PKG
+fi
+
 find $PKG -print0 | xargs -0 file | grep -e "executable" -e "shared object" | grep ELF \
   | cut -f 1 -d : | xargs strip --strip-unneeded 2> /dev/null || true