First implementation of per-chunk CRC32 check. This is triggered

- by the right-click+Force Check on files.
- when a global hash on a downloaded file does not match the announced hash.

When a CRC map check is ordered, the CRC map is requested to one of the sources for the current file download.
When received, all downloaded chunks are checked w.r.t the reference CRC and marked as not done if the CRCs do not match.
The exchange of CRC32 map and requests has been tested, as well as CRC map checking during download (force check).

To be implemented soon:
    - caching of CRC32 maps (although these are fast to compute)
    - CRC32 map packets for normal downloads. For now these work only for turtle tunnels.
    - handling of errors if the CRC never comes. For now, the download will stay stuck in "Checking..." mode.

So, don't play too much with the force check feature for now...





git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@3310 b45a01b8-16f6-495d-af2f-9b41ad6348cc

libretroshare/src/ft/ftchunkmap.h

@@ -144,6 +144,9 @@ class ChunkMap
 		//
 		static void buildPlainMap(uint64_t size,CompressedChunkMap& map) ;
 
+		/// Computes the number of chunks for the given file size.
+		static uint32_t getNumberOfChunks(uint64_t size) ;
+		
 		/// This function is used by the parent ftFileProvider to know whether the chunk can be sent or not.
 		bool isChunkAvailable(uint64_t offset, uint32_t chunk_size) const ;
 
@@ -162,6 +165,7 @@ class ChunkMap
 		bool isComplete() const { return _file_is_complete ; }
 
 		void getChunksInfo(FileChunksInfo& info) const ;
+
 	protected:
 		/// handles what size the last chunk has.
 		uint32_t sizeOfChunk(uint32_t chunk_number) const ;