Allow RBUG to start blocked

It is sometimes useful to examine the first frame or and early frame of a
quickly executing and non-repeating application, this chain introduces a new
environment variable that is checked when creating contexts.  If
GALLIUM_RBUG_START_BLOCKED is set, then each context that is created is started
in a blocked state.  This allows time to connect rbug before anything is
rendered in the context.
1 file changed