Start tracking composer.lock in git

@naderman seems to think this is a good idea, and he seems to know a thing or two about Composer. On a serious note, this should be helpful so we can track test suite status against specific dependency versions.

Author: jmikola

.gitignore

@@ -3,6 +3,4 @@ tools/sandbox/Hydrators/*
 tests/Proxies/*
 tests/Hydrators/*
 phpunit.xml
-vendor
-composer.lock
-composer.phar
+vendor/