Consistently use TODO for to-dos.

lib/CMakeLists.txt

diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 262074d..358e212 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -143,7 +143,7 @@
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR}
   ${CMAKE_CURRENT_BINARY_DIR}/..)
 
-# XXX: distribute instead?
+# TODO: distribute instead?
 #ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/zip_err_str.c
 #  COMMAND sh ${CMAKE_CURRENT_SOURCE_DIR}/make_zip_err_str.sh
 #    ${CMAKE_CURRENT_SOURCE_DIR}/zip.h