Consider collision avoidance on create

[dereuromark]

https://github.com/cakephp/phinx/blob/0.x/src/Phinx/Console/Command/Create.php
You could apply sth similar here we currently evaluate for Migrations:
cakephp/migrations#773

When you generate multiple ones, this will otherwise create exceptions when reading/using.

[MasterOdin]

Interesting bug, not sure how often it'd come up before now. I think that my preferred solution would be to take the timestamp, and if there's an existing one, then just increment it by 1 until we hit a timestamp that's valid. This would be BC, and that I don't think anyone really cares about the timestamp prefix value beyond it just enforcing the right numerical order of files in the file tree / migration list.

[dereuromark]

Isnt that exactly how I fixed it in the linked PR? :)

[MasterOdin]

Hah, for some reason I swear I thought that your PR was appending an incrementing ## to the end of the timestamp if there was a collision. My bad, yeah, that looks pretty perfect to port into phinx as well.