* ALL: Better announce system

* ALL: Better announce system

  - The SAP handler now runs in a separate thread.
  - RTP sessions can be announced with sap (sdp=sap://,name=...)
	TODO: Make this more configurable
  - Better SDP generation (the timestamp problem is not resolved)
	About this, there is a problem : as, for a RTP session, the URI
        is the complete SDP, if the session is recreated, as the URI has
        changed, a new item is added to the playlist
  - Experimental flow control algorithm :
       It does not follow the "Recommended" implementation, as it needs
       to count the sessions (to achieve this, we should make this work
       together with the SAP listener)
       It is disabled by default (use --sap-flow-control to enable).
       When it is disabled, sap announcement interval is set by --sap-interval

* src/misc/net.c : created net_ReadNonBlock
* sap.c : Fixed memory problem