Use ":" to separate package and executable name in pub global run

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="96" height="96"hspace="10"> Issue by munificent
Originally opened as dart-lang/sdk#19863

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This makes it consistent with pub run.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="48" height="48"hspace="10"> Comment by munificent

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Added Started label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/46275?v=3" align="left" width="48" height="48"hspace="10"> Comment by munificent

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This is done now.

Sharon, I also added a little convenience here. If you leave off a script name, it assumes the same name as the package. So doing:

$ pub global run foo

Means "run bin/foo.dart from the globally activated version of foo". Do you think you could update the docs to mention that? Should I file a bug?

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cc @Sfshaza.
Added Fixed label.