WIP - Add Debian init script

Hi,

this adds a Debian init.d script. In its current state in it's only useful for *real* Debian distros.
Also it has some customizations like bouncing the version and a hardcoded `$GOPATH`, because I couldn't get it to build on `Squeeze` otherwise.
In order to support Ubuntu, we would have to add an upstart script conditionally instead of the systemv one.
I also moved up the `DEB` block in https://github.com/Jimdo/heka/blob/3ad99212f28b9bd5a251003f056fc26e8dc94a71/CMakeLists.txt to be before the `include(CPack)`. Otherwise the `CPACK_DEBIAN_*` vars are not picked up properly.