updated symfony to version 2.6.1

2.6.1 (2014-12-03)

bug #12823 [DependencyInjection] fix PhpDumper (nicolas-grekas)
bug #12811 Configure firewall's kernel exception listener with configured entry point or a default entry point (rjkip)
bug #12770 [Filesystem] fix lock file permissions (nicolas-grekas)
bug #12784 [DependencyInjection] make paths relative to DIR in the generated container (nicolas-grekas)
bug #12716 [ClassLoader] define constant only if it wasn't defined before (xabbuh)
2.6.0 (2014-11-28)