Installing an app a second time should skip if already installed

[lythix]

Issuing an install command for a package should not download and install a package if that version is already installed.
Some fallback behaviour could be to do a repair, or upgrade.
If the same version (or the latest version) is installed, there is no reason to re-download and install the app.

[megamorf]

This is a duplicate of #216.

[denelon]

Duplicate of #216, and thanks @megamorf

[ghost]

Hi! We've identified this issue as a duplicate of another one that already exists on this Issue Tracker. This specific instance is being closed in favor of tracking the concern over on the referenced thread. Thanks for your report!