patch 7.4.915
Problem:    When removing from 'path' and then adding, a comma may go missing.
            (Malcolm Rowe)
Solution:   Fix the check for P_ONECOMMA. (closes #471)
diff --git a/src/testdir/test_options.ok b/src/testdir/test_options.ok
index a2e1494..0773152 100644
--- a/src/testdir/test_options.ok
+++ b/src/testdir/test_options.ok
@@ -1,2 +1,3 @@
 result
 ok
+foo,,bar