implemented verbose output

src/Composer/EventDispatcher/EventDispatcher.php

@@ -170,8 +170,12 @@ class EventDispatcher
                     throw $e;
                 }
             } else {
-                $args = implode(' ', array_map(array('Composer\Util\ProcessExecutor','escape'), $event->getArguments()));
-                if (0 !== ($exitCode = $this->process->execute($callable . ($args === '' ? '' : ' '.$args)))) {
+                $args = implode(' ', array_map(array('Composer\Util\ProcessExecutor', 'escape'), $event->getArguments()));
+                $exec = $callable . ($args === '' ? '' : ' '.$args);
+                if ($this->io->isVerbose()) {
+                    $this->io->writeError(sprintf('> %s', $exec));
+                }
+                if (0 !== ($exitCode = $this->process->execute($exec))) {
                     $this->io->writeError(sprintf('<error>Script %s handling the %s event returned with an error</error>', $callable, $event->getName()));
 
                     throw new \RuntimeException('Error Output: '.$this->process->getErrorOutput(), $exitCode);