Allow sepgsql labels to depend on object name.

The main change here is to call security_compute_create_name_raw()
rather than security_compute_create_raw().  This ups the minimum
requirement for libselinux from 2.0.99 to 2.1.10, but it looks
like most distributions will have picked that up before 9.3 is out.

KaiGai Kohei
sepgsql: Documentation improvements.

Fixes by me, per griping by Thom Brown.