first stab at sparse files support

include/libtorrent/storage.hpp

@@ -135,7 +135,7 @@ namespace libtorrent
 		bool verify_resume_data(entry& rd, std::string& error);
 
 		bool is_allocating() const;
-		void allocate_slots(int num_slots);
+		bool allocate_slots(int num_slots);
 		void mark_failed(int index);
 
 		unsigned long piece_crc(
@@ -165,6 +165,8 @@ namespace libtorrent
 		// of unassigned pieces and -1 is unallocated
 		void export_piece_map(std::vector<int>& pieces) const;
 
+		bool compact_allocation() const;
+
 	private:
 		class impl;
 		std::auto_ptr<impl> m_pimpl;