/* The content of the .h.in file is automatically updated by
 * configure, so in theory the .h.in file does not need to be
 * in the source tree, but the file must exist, otherwise
 * automake fails.
 *
 * The .h.in is a work-around to AC_DEFINE_UNQUOTED only working
 * with fixed variable names when using AC_CONFIG_HEADERS.
 * configure writes the #undef statements to the .h.in file, so
 * that when AC_OUTPUT is invoked, the .h file is created from
 * the .h.in file, with the appropriate #define's being set.
 */