Detect another PostgreSQL backend

I know this is ugly, but I don't see better way.

Once we stop supporting Django 1.7, this code will be subject to major
cleanup and better solution could be found.

Fixes #869
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/boolean_sum.py

@@ -33,6 +33,8 @@ def get_template():
     '''
     if 'psycopg2' in settings.DATABASES['default']['ENGINE']:
         return '%(function)s(%(field)s::int)'
+    if 'postgre' in settings.DATABASES['default']['ENGINE']:
+        return '%(function)s(%(field)s::int)'
     return '%(function)s(%(field)s)'