setup.py: Use sage -t --optional=sage to avoid errors with sage from conda

Author: Matthias Koeppe

setup.py

@@ -28,10 +28,10 @@ def readfile(filename):
 class SageTest(TestCommand):
     def run_tests(self):
         import os, sys
-        errno = os.system("sage -t --force-lib sage_widget_adapters")
+        errno = os.system("sage -t --force-lib --optional=sage sage_widget_adapters")
         if errno != 0:
             sys.exit(1)
-        errno = os.system("sage -t --force-lib sage_combinat_widgets")
+        errno = os.system("sage -t --force-lib --optional=sage sage_combinat_widgets")
         if errno != 0:
             sys.exit(1)