Inline more of the packing code: API calls are now the only part that can't be inlined.  Special case single-character format strings to avoid __pack_init / __pack_next.
Move pack/unpack methods into the extension API, because extensions shouldn't link with the WiredTiger library.
While in the area, make doxygen comment formatting consistent: block comments should have a blank first line.
../src/log/log.c:32:2: error: 'size' may be used uninitialized in this function [-Werror=uninitialized]