Title: Add unit test to assert ":A" is a valid title value

Mostly to catch regressions. While this is an invalid title,
it is valid as syntax when creating a Title *object*, the actual
page title itself does not allow leading colons.

Change-Id: Idbe8a3bfe487926c5fc8bdcfa69a957fc9d0bc49
Merge "Title: Add unit test to assert ":A" is a valid title value"