Unity: Fix solution/project files for nested directories.

[Unity3d](http://unity3d.com/)

By having the leading `/` infront of the `*` makes these types of files relative to the directory the gitignore is in. If you create a Unity project inside of a git repository Unity forces you to create a new directory, thus not picking up these files.

A common pattern for version controlling Unity is

1. Create git repo on github with gitignore template
2. Clone
3. Create a Unity project inside the git repo (which is forced into a new directory)

This pull request will accommodate for multiple projects in one repository, or the pattern outlined above, while leaving other workflows unharmed