Sbig ethernet support

Verified to work with ST-8XE and STX-16803.

Due to requirement of START_EXPOSURE2 for newer cameras (works for older ones as well) it requires newer python bindings to the sbig library (which seemingly is only provided in form of an dynamic library now).

Also one needs a certain LD_PRELOAD library for ethernet to work, since sbig wasn't able to use setsockopt correctly (at least not on modern linux kernels).