uberjar should not rebuild the jar with :auto-clean false and no changes

[arr-ee]

Follow up for irc conversation.

With lein 2.5.1,

• run lein new app testapp
• add :auto-clean false to project.clj (I also tried adding it to uberjar profile`)
• run lein uberjar twice
• Compilation runs only once, but jars are regenerated every time

This is very annoying in large-ish projects, especially when you need to run uberjar several times in a row (i.e. when building packages).