os: example trace policy-modules
enable trace policy-module loading in demo
base: add name accessor method to RPC struct

This method may be used to get the actual name of the
corresponding RPC-function.
rename Policy to Policy_module
rename Msg_buf_base to Msgbuf_base
fix wrong condition source.is_valid
fix bootstrap problem (inhibit_tracing, !this)
inhibit tracing in core
explicitly call env() in _main
add Trace::Rpc_call
add test-thread to test/trace
XXX debug msg -> rewriting addr in policy_module
XXX trace_test runscript