feature #105 Allow last LTS version to be installed. (94noni)

This PR was squashed before being merged into the 1.0-dev branch (closes #105).

Discussion
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Allow last LTS version to be installed.

Hi,

I just wanted to add the possibility to install the latest Symfony LTS version directly via the installer (new command).

Docs PR symfony/symfony-docs#5032

Feedbacks welcome :)

Commits
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6c08849 Allow last LTS version to be installed.

Author: javiereguiluz

README.md

@@ -45,7 +45,21 @@ $ symfony new my_project
 $ php symfony.phar new my_project
 ```
 
-**2. Start a new project based on a specific Symfony branch**
+**2. Start a new project with the latest Symfony LTS version**
+
+Execute the `new` command and provide the name of your project as the first
+argument and `lts` as the second argument. The installer will automatically
+select the most recent LTS version available:
+
+```bash
+# Linux, Mac OS X
+$ symfony new my_project lts
+
+# Windows
+$ php symfony.phar new my_project lts
+```
+
+**3. Start a new project based on a specific Symfony branch**
 
 Execute the `new` command and provide the name of your project as the first
 argument and the branch number as the second argument. The installer will
@@ -59,7 +73,7 @@ $ symfony new my_project 2.3
 $ php symfony.phar new my_project 2.3
 ```
 
-**3. Start a new project based on a specific Symfony version**
+**4. Start a new project based on a specific Symfony version**
 
 Execute the `new` command and provide the name of your project as the first
 argument and the exact Symfony version as the second argument:

src/Symfony/Installer/AboutCommand.php

@@ -54,6 +54,11 @@ protected function execute(InputInterface $input, OutputInterface $output)
 
    <comment>%s new blog</comment>
 
+ To create a new project called <info>blog</info> in the current directory using
+ the <info>long term support version</info> of Symfony, execute the following command:
+
+   <comment>%s new blog lts</comment>
+
  To base your project on a <info>specific Symfony branch</info>, append the branch
  number at the end of the command:
 

src/Symfony/Installer/NewCommand.php

@@ -137,6 +137,11 @@ private function checkSymfonyVersionIsInstallable()
             return $this;
         }
 
+        // 'lts' is a special version name that refers to the current long term support version
+        if ('lts' === $this->version) {
+            return $this;
+        }
+
         // validate semver syntax
         if (!preg_match('/^2\.\d(?:\.\d{1,2})?$/', $this->version)) {
             throw new \RuntimeException('The Symfony version should be 2.N or 2.N.M, where N = 0..9 and M = 0..99');