* don't show warning if add-on is already installed.  * don't show warning if add-on can't be installed. 
* don't show warning if add-on is already installed. 
* don't show warning if add-on can't be installed. 

git-svn-id: c0b6191cc07a4792c57db861536a2f9523dc26f7@610 b58a29cf-3064-46da-94c6-1c29cc75c8e5

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