Improved CRC32Map checking in several ways:

- servers now compute the map in a separate thread
- CRC32Maps are kept in cache for 30 mins
- CRC32Maps requests cannot be used to overflood a server anymore since their number is limited.
- Transfer modules now send keep alive packets to maintain tunnels when asking for a CRC32Map



git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@4661 b45a01b8-16f6-495d-af2f-9b41ad6348cc

libretroshare/src/ft/ftfilecreator.h

@@ -113,12 +113,6 @@ class ftFileCreator: public ftFileProvider
 		virtual void getAvailabilityMap(CompressedChunkMap& cmap) ;
 		void setAvailabilityMap(const CompressedChunkMap& cmap) ;
 
-		// Provides a complete per-chunk CRC32 map to client who want to check their data.
-		// This is overloads ftFileProvider, but returns false, because we can't ensure that unchecked chunks
-		// will provide a CRC32 that is faithful to the original hash.
-		//
-		virtual bool getCRC32Map(CRC32Map& /*crc_map*/) { return false ; }
-
 		// This is called when receiving the availability map from a source peer, for the file being handled.
 		//
 		void setSourceMap(const std::string& peer_id,const CompressedChunkMap& map) ;