fix some 'format not a string literal's

libtorrent/src/session_impl.cpp

@@ -4948,7 +4948,7 @@ retry:
 		char buf[450];
 		snprintf(buf, sizeof(buf), "%s: %s\n", time_now_string(), usr);
 		// printf is the bitcoin/util.h logger
-		printf(buf);
+		printf("%s", buf);
 		//(*m_logger) << buf;
 	}
 #endif
@@ -6516,7 +6516,7 @@ retry:
 			char buf[1280];
 			snprintf(buf, sizeof(buf), "%s: %s\n", time_now_string(), usr);
 			// printf is the bitcoin/util.h logger
-			printf(buf);
+			printf("%s", buf);
 			//(*m_ses.m_logger) << buf;
 		}
 #endif

libtorrent/src/torrent.cpp

@@ -8632,7 +8632,7 @@ namespace libtorrent
 			, to_hex(info_hash().to_string()).substr(0, 6).c_str(), usr);
 		//(*m_ses.m_logger) << buf;
 		// [MF]
-		printf(buf);
+		printf("%s", buf);
 	}
 #endif