symbol preprocessing (trunk only)

Clean up the preprocessing associated with the
loadable symbol stuff.

Base it on new LOADSYMSETS, rather than on the
previously existing ASCIIGRAPH preprocessor define.

sys/unix/unixmain.c

@@ -370,7 +370,7 @@ char *argv[];
 		case 'I':
 		case 'i':
 			if (!strncmpi(argv[0]+1, "IBM", 3)) {
-#ifdef ASCIIGRAPH
+#ifdef LOADSYMSETS
 				load_symset("IBMGraphics", PRIMARY);
 				load_symset("RogueIBM", ROGUESET);
 				switch_symbols(TRUE);
@@ -380,7 +380,7 @@ char *argv[];
 	    /*  case 'D': */
 		case 'd':
 			if (!strncmpi(argv[0]+1, "DEC", 3)) {
-#ifdef ASCIIGRAPH
+#ifdef LOADSYMSETS
 				load_symset("DECGraphics", PRIMARY);
 				switch_symbols(TRUE);
 #endif