Set script name correctly when invoked via sysv-style init

The CentOS initscript is designed to be symlinked when creating multiple instances. It examines its own filename to determine the name of the instance. However, when invoked via runlevel scripts (i.e. on boot) there's another level of symlinking that breaks this assumption:

    /etc/init.d/celeryd-helloworld -> /etc/init.d/celeryd
instance is named "celeryd-helloworld"

    /etc/rc2.d/S50celeryd-helloworld -> /etc/init.d/celeryd-helloworld -> /etc/init.d/celeryd
instance is named "S50celeryd-helloworld"

Attached pull request fixes this so the instance name is set consistently.