Using the currently running PHP executable for launching scripts

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | -
| License       | BSD-3-Clause
| Doc PR        | -

Some hard-coded **php** strings for launching scripts including the composer.json file may cause an error as the following:

```shell
$ BEAR_DB_ID=bear BEAR_DB_PASSWORD=bear /usr/bin/php5 /path/tocomposer.phar install
Installing dependencies (including require-dev) from lock file
Nothing to install or update
Generating autoload files
PHP Parse error:  syntax error, unexpected '[', expecting ')' in /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bootstrap/autoload.php on line 23
PHP Stack trace:
PHP   1. {main}() /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bin/compiler.php:0

Parse error: syntax error, unexpected '[', expecting ')' in /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bootstrap/autoload.php on line 23

Call Stack:
    0.0003     640640   1. {main}() /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bin/compiler.php:0

Script php apps/Sandbox/bin/compiler.php handling the post-autoload-dump event returned with an error


                                                                                
  [RuntimeException]                                                            
  Error Output: PHP Parse error:  syntax error, unexpected '[', expecting ')'   
  in /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bootstrap/autoload.php   
  on line 23                                                                    
  PHP Stack trace:                                                              
  PHP   1. {main}() /home/iteman/git/koriym/BEAR.Package/apps/Sandbox/bin/comp  
  iler.php:0                                                                    
                                                                                
                                                                                


install [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--no-plugins] [--no-custom-installers] [--no-scripts] [--no-progress] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader]
```

In my case, */home/iteman/apps/phpenv/shims/php* (PHP 5.3.8) is used as the **php** executable.