python/pytz: Add python3 support.

Signed-off-by: David Spencer <idlemoor@slackbuilds.org>

python/pytz/README

@@ -3,3 +3,8 @@ accurate and cross platform timezone calculations using Python 2.3
 or higher. It also solves the issue of ambiguous times at the end
 of daylight savings, which you can read more about in the Python
 Library Reference (datetime.tzinfo).
+
+python3 is an optional dependency.  You need to set PYTHON3=yes,
+for example:
+
+  PYTHON3=yes ./pytz.SlackBuild

python/pytz/pytz.SlackBuild

@@ -57,6 +57,11 @@ find -L . \
 
 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 | xargs file | grep -e "executable" -e "shared object" | grep ELF \
   | cut -f 1 -d : | xargs strip --strip-unneeded 2> /dev/null || true