- set priority of vc thread depending if client is a real-time task or not
- initiate client callbacks with timeout 0

- include/ARCH-x86/l4con.h:
  - GRAPH_* macros used internally only
  - CON_E* error macros could (mostly) be mapped to L4_E*
  - CON_CLOSED, CON_CLOSING, CON_OPENING, CON_MASTER macros are for internal use
    only
  - ALL macros should begin with L4CON_
