Don't add Duplicate Commands to Command History

[LaurenceWarne]

Hi, this PR makes it so that duplicate commands are not added to the command history (a command is only added to the history ring if it doesn't equal the most recent command).

Related is: #1654, but it has the same effect for projectile-test-project, projectile-compile-project and so on.

Thanks!

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Thanks!

[bbatsov]

Thanks!