When no version is provided, the latest stable version of Symfony is installed
feature #37 When no version is provided, the latest stable version of Symfony is installed (javiereguiluz)

This PR was merged into the 1.0-dev branch.

Discussion
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When no version is provided, the latest stable version of Symfony is installed

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #2
| License       | MIT
| Doc PR        | -

Commits
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1e9896c When no version is provided, the latest stable version of Symfony is installed