Duplicate slug when we create same name post and page.

[datta.parad]

steps for reproduce the error

1) create post with the name "test"
you will get the slug for post is "test"

2) create page with the name "test"
You will get the slug for page is also "test"

if we set permalink to %postname%, this both get conflict.

[SergeyBiryukov]

Duplicate of #13459.