compile PHAR from folder without dev dependencies

currently "composer.phar" ships a autoloading classmap for PHPUnit.
that's because composer's own development dependencies are installed (composer install -q) and autoloading maps are created. The PHAR compiler excludes "Tests" folders and PHPUnit itself from vendor folders, but includes the autoloading maps.

By appending "--no-dev" PHPUnit is not installed and an empty map is created.
This empty map is then included by the PHAR compiler.

And this leads directly to the next issue: "exclude empty autloading map files from inclusion into a PHAR". Including empty autoloading strategies is waste. But that's a PHAR compiler issue.
Merge pull request #65 from jakoch/patch-1

compile PHAR from folder without dev dependencies