* Replace variadic debugpline() with fixed argument debugpline0(str),
debugpline1(fmt,arg), and so on so that C99 support isn't required;
* showdebug() becomes a function rather than a macro and handles a
bit more;
* two debugpline() calls in light.c have been changed to impossible();
* DEBUGFILES macro (in sys.c) can substitute for SYSCF's DEBUGFILES
setting in !SYSCF configuration (I hope that's temporary).
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