Makefile: Drop TODO.txt from dist
tifflike: Fix compiler warnings with libtiff < 4

The TIFFDataType enum of libtiff < 4 doesn't include the BigTIFF type
values.  There's no reason we need to use the enum, so drop it.
mirax: Propagate original GKeyFileError when keyfile fetch fails
test/driver: Print total size of delta files after packing